Fix #1269 A bug on the metric calculation inside async API clients

[seratch]

This pull request resolves #1269, thank you so much @gunrein !

The bug had been affecting only the output of the visible metrics data for developers. The internal smart rate limiter mechanism does not use the data at all, so the impact of the misbehavior should be relatively small.

Category (place an x in each of the [ ])

• [ ] bolt (Bolt for Java)
• [ ] bolt-{sub modules} (Bolt for Java - optional modules)
• [x] slack-api-client (Slack API Clients)
• [ ] slack-api-model (Slack API Data Models)
• [ ] *slack-api--kotlin-extension** (Kotlin Extensions for Slack API Clients)
• [ ] slack-app-backend (The primitive layer of Bolt for Java)

Requirements

Please read the Contributing guidelines and Code of Conduct before creating this issue or pull request. By submitting, you agree to those rules.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (44676f5) 74.33% compared to head (bc93fa4) 74.35%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1270 +/- ## ============================================ + Coverage 74.33% 74.35% +0.01% - Complexity 4124 4125 +1 ============================================ Files 443 443 Lines 13092 13080 -12 Branches 1324 1323 -1 ============================================ - Hits 9732 9725 -7 + Misses 2588 2582 -6 - Partials 772 773 +1 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.