zulip-bots: Add `BotHandler` Protocol.

[LoopThrough-i-j]

• zulip-bots: Add CommonStorage Protocol.

  • The CommonStorage Protocol is created to add a Common type to all Storage Classes.
  • The Storages used in BotHandlers are typed as CommonStorage

  Note: Protocol is imported from typing_extensions as typingdoesn't provide Protocol for python <= 3.7.

• zulip-bots: Add BotHandler Protocol.

  The BotHandler Protocol has methods which allow any of the Current BotHandlers to use BotHandler Protocol as a mypy type.

  Fixes part of #639

• zulip-bots: Set bot_handler type to BotHandler.

  • Set bot_handler type to BotHandler.
  • Fix mypy issues in improperly typed variables and returns.

  Fixes #639

[LoopThrough-i-j]

@neiljp thanks for pointing out some improvements. I had actually added inherited the BotHandler class and added some helper functions in the BotHandler, confused by the innumerable number of errors thrown by the bots after the 2nd commit, which I slowly debugged and figured out and then considered keeping the BotHandler the same.

[andersk]

In order to use this in zulip/zulip, we also need to adjust zulip_bots.lib.extract_query_without_mention to take BotHandler instead of ExternalBotHandler. There may be other such adjustments that make sense.

[LoopThrough-i-j]

In order to use this in zulip/zulip, we also need to adjust zulip_bots.lib.extract_query_without_mention to take BotHandler instead of ExternalBotHandler. There may be other such adjustments that make sense.

Thanks, I didn't know. Will get things fixed soon.