Ensure slackbot doesn't crash when multiple messages are sent at the same time by different users

Seems okay though we get some errors in the logs:
2023-09-27 16:06:35 [   DEBUG] Received message (type: TEXT, data: {"envelope_id":"25f8c8b5-497d-46ee-924c-690a110e7ae9","payload":{"token":"OEqSunrvpkP80Su25M5fdu4W","team_id":"T057SAAS0K0","api_app_id":"A05RS0R47SA","event":{"client_msg_id":"d702f10a-7661-457b-8c3f-92e6a4964759","type":"app_mention","text":"<@U05RJ4R1V1D> what?","user":"U05BM5KRRK9","ts":"1695827194.721599","blocks":[{"type":"rich_text","block_id":"xLYe","elements":[{"type":"rich_text_section","elements":[{"type":"user","user_id":"U05RJ4R1V1D"},{"type":"text","text":" what?"}]}]}],"team":"T057SAAS0K0","channel":"C05T2SU35FX","event_ts":"1695827194.721599"},"type":"event_callback","event_id":"Ev05U8B02J3E","event_time":1695827194,"authorizations":[{"enterprise_id":null,"team_id":"T057SAAS0K0","user_id":"U05RJ4R1V1D","is_bot":true,"is_enterprise_install":false}],"is_ext_shared_channel":false,"event_context":"4-eyJldCI6ImFwcF9tZW50aW9uIiwidGlkIjoiVDA1N1NBQVMwSzAiLCJhaWQiOiJBMDVSUzBSNDdTQSIsImNpZCI6IkMwNVQyU1UzNUZYIn0"},"type":"events_api","accepts_response_payload":false,"retry_attempt":0,"retry_reason":""}, extra: , session: s_393286281)
2023-09-27 16:06:35 [   DEBUG] A new message enqueued (current queue size: 1, session: s_393286281)
2023-09-27 16:06:35 [   DEBUG] Message processing started (type: events_api, envelope_id: 25f8c8b5-497d-46ee-924c-690a110e7ae9, session: s_393286281)
2023-09-27 16:06:35 [    INFO] Received an events_api request
2023-09-27 16:06:35 [   DEBUG] Sending a message: {"envelope_id": "25f8c8b5-497d-46ee-924c-690a110e7ae9"} from session: s_393286281
2023-09-27 16:06:35 [   DEBUG] Event: {'client_msg_id': 'd702f10a-7661-457b-8c3f-92e6a4964759', 'type': 'app_mention', 'text': '<@U05RJ4R1V1D> what?', 'user': 'U05BM5KRRK9', 'ts': '1695827194.721599', 'blocks': [{'type': 'rich_text', 'block_id': 'xLYe', 'elements': [{'type': 'rich_text_section', 'elements': [{'type': 'user', 'user_id': 'U05RJ4R1V1D'}, {'type': 'text', 'text': ' what?'}]}]}], 'team': 'T057SAAS0K0', 'channel': 'C05T2SU35FX', 'event_ts': '1695827194.721599'}
2023-09-27 16:06:35 [    INFO] Reacting with clock emoji.
2023-09-27 16:06:35 [   DEBUG] Sending a request - url: POST https://www.slack.com/api/reactions.add, params: {'channel': 'C05T2SU35FX', 'name': 'clock2', 'timestamp': '1695827194.721599'}, files: {}, data: {}, json: {}, proxy: {}, headers: {'Content-Type': 'application/x-www-form-urlencoded', 'Authorization': '(redacted)', 'User-Agent': 'Python/3.11.4 slackclient/3.22.0 Darwin/21.6.0'}
2023-09-27 16:06:35 [   DEBUG] Received message (type: TEXT, data: {"envelope_id":"5f223574-c02c-4e08-81ae-474945a4377b","payload":{"token":"OEqSunrvpkP80Su25M5fdu4W","team_id":"T057SAAS0K0","context_team_id":"T057SAAS0K0","context_enterprise_id":null,"api_app_id":"A05RS0R47SA","event":{"client_msg_id":"d702f10a-7661-457b-8c3f-92e6a4964759","type":"message","text":"<@U05RJ4R1V1D> what?","user":"U05BM5KRRK9","ts":"1695827194.721599","blocks":[{"type":"rich_text","block_id":"xLYe","elements":[{"type":"rich_text_section","elements":[{"type":"user","user_id":"U05RJ4R1V1D"},{"type":"text","text":" what?"}]}]}],"team":"T057SAAS0K0","channel":"C05T2SU35FX","event_ts":"1695827194.721599","channel_type":"channel"},"type":"event_callback","event_id":"Ev05TZ89JU1L","event_time":1695827194,"authorizations":[{"enterprise_id":null,"team_id":"T057SAAS0K0","user_id":"U05RJ4R1V1D","is_bot":true,"is_enterprise_install":false}],"is_ext_shared_channel":false,"event_context":"4-eyJldCI6Im1lc3NhZ2UiLCJ0aWQiOiJUMDU3U0FBUzBLMCIsImFpZCI6IkEwNVJTMFI0N1NBIiwiY2lkIjoiQzA1VDJTVTM1RlgifQ"},"type":"events_api","accepts_response_payload":false,"retry_attempt":0,"retry_reason":""}, extra: , session: s_393286281)
2023-09-27 16:06:35 [   DEBUG] A new message enqueued (current queue size: 1, session: s_393286281)
2023-09-27 16:06:35 [   DEBUG] Message processing started (type: events_api, envelope_id: 5f223574-c02c-4e08-81ae-474945a4377b, session: s_393286281)
2023-09-27 16:06:35 [    INFO] Received an events_api request
2023-09-27 16:06:35 [   DEBUG] Response: <slack_sdk.socket_mode.response.SocketModeResponse object at 0x43fed2010>
2023-09-27 16:06:35 [   DEBUG] Sending a message: {"envelope_id": "5f223574-c02c-4e08-81ae-474945a4377b"} from session: s_393286281
2023-09-27 16:06:35 [   DEBUG] Event: {'client_msg_id': 'd702f10a-7661-457b-8c3f-92e6a4964759', 'type': 'message', 'text': '<@U05RJ4R1V1D> what?', 'user': 'U05BM5KRRK9', 'ts': '1695827194.721599', 'blocks': [{'type': 'rich_text', 'block_id': 'xLYe', 'elements': [{'type': 'rich_text_section', 'elements': [{'type': 'user', 'user_id': 'U05RJ4R1V1D'}, {'type': 'text', 'text': ' what?'}]}]}], 'team': 'T057SAAS0K0', 'channel': 'C05T2SU35FX', 'event_ts': '1695827194.721599', 'channel_type': 'channel'}
2023-09-27 16:06:35 [    INFO] Reacting with clock emoji.
2023-09-27 16:06:35 [   DEBUG] Sending a request - url: POST https://www.slack.com/api/reactions.add, params: {'channel': 'C05T2SU35FX', 'name': 'clock2', 'timestamp': '1695827194.721599'}, files: {}, data: {}, json: {}, proxy: {}, headers: {'Content-Type': 'application/x-www-form-urlencoded', 'Authorization': '(redacted)', 'User-Agent': 'Python/3.11.4 slackclient/3.22.0 Darwin/21.6.0'}
2023-09-27 16:06:35 [   DEBUG] Received the following response - status: 200, headers: {'Date': 'Wed, 27 Sep 2023 15:06:35 GMT', 'Server': 'Apache', 'Vary': 'Accept-Encoding', 'x-slack-req-id': '70c333f3920576eb615e2861de95464e', 'x-content-type-options': 'nosniff', 'x-xss-protection': '0', 'Pragma': 'no-cache', 'Cache-Control': 'private, no-cache, no-store, must-revalidate', 'Expires': 'Sat, 26 Jul 1997 05:00:00 GMT', 'Content-Type': 'application/json; charset=utf-8', 'x-accepted-oauth-scopes': 'reactions:write', 'x-oauth-scopes': 'commands,im:history,reactions:write,chat:write,im:write,emoji:read,reactions:read,app_mentions:read,im:read,incoming-webhook,channels:history,chat:write.public,users.profile:read', 'Access-Control-Expose-Headers': 'x-slack-req-id, retry-after', 'Access-Control-Allow-Headers': 'slack-route, x-slack-version-ts, x-b3-traceid, x-b3-spanid, x-b3-parentspanid, x-b3-sampled, x-b3-flags', 'strict-transport-security': 'max-age=31536000; includeSubDomains; preload', 'x-slack-unique-id': 'ZRRE-6cNCK7gHv_JBduJCAAAABM', 'x-slack-backend': 'r', 'referrer-policy': 'no-referrer', 'Access-Control-Allow-Origin': '*', 'Content-Length': '38', 'Via': '1.1 slack-prod.tinyspeck.com, envoy-www-iad-eptiywew, envoy-edge-lhr-milphoza', 'x-envoy-attempt-count': '1', 'x-envoy-upstream-service-time': '107', 'x-backend': 'main_normal main_canary_with_overflow main_control_with_overflow', 'x-server': 'slack-www-hhvm-main-iad-pxjy', 'x-slack-shared-secret-outcome': 'no-match', 'x-edge-backend': 'envoy-www', 'x-slack-edge-shared-secret-outcome': 'no-match'}, body: {'ok': False, 'error': 'already_reacted'}
2023-09-27 16:06:35 [   ERROR] Something went wrong in processing a Slack request.
Payload: {'token': 'OEqSunrvpkP80Su25M5fdu4W', 'team_id': 'T057SAAS0K0', 'context_team_id': 'T057SAAS0K0', 'context_enterprise_id': None, 'api_app_id': 'A05RS0R47SA', 'event': {'client_msg_id': 'd702f10a-7661-457b-8c3f-92e6a4964759', 'type': 'message', 'text': '<@U05RJ4R1V1D> what?', 'user': 'U05BM5KRRK9', 'ts': '1695827194.721599', 'blocks': [{'type': 'rich_text', 'block_id': 'xLYe', 'elements': [{'type': 'rich_text_section', 'elements': [{'type': 'user', 'user_id': 'U05RJ4R1V1D'}, {'type': 'text', 'text': ' what?'}]}]}], 'team': 'T057SAAS0K0', 'channel': 'C05T2SU35FX', 'event_ts': '1695827194.721599', 'channel_type': 'channel'}, 'type': 'event_callback', 'event_id': 'Ev05TZ89JU1L', 'event_time': 1695827194, 'authorizations': [{'enterprise_id': None, 'team_id': 'T057SAAS0K0', 'user_id': 'U05RJ4R1V1D', 'is_bot': True, 'is_enterprise_install': False}], 'is_ext_shared_channel': False, 'event_context': '4-eyJldCI6Im1lc3NhZ2UiLCJ0aWQiOiJUMDU3U0FBUzBLMCIsImFpZCI6IkEwNVJTMFI0N1NBIiwiY2lkIjoiQzA1VDJTVTM1RlgifQ'}.
The request to the Slack API failed. (url: https://www.slack.com/api/reactions.add, status: 200)
The server responded with: {'ok': False, 'error': 'already_reacted'}
2023-09-27 16:06:35 [   ERROR] Failed to run a request listener: The request to the Slack API failed. (url: https://www.slack.com/api/reactions.add, status: 200)
The server responded with: {'ok': False, 'error': 'already_reacted'}, session: s_393286281
alan-turing-institute / reginald

Ensure slackbot doesn't crash when multiple messages are sent at the same time by different users #94
