health: move to mypy

[WilliamBergamin]

Summary

This PR aims to follow the Bolt Pythons #1130

MyPy was found to execute much fast the PyType in this project, these changes adapt the project to use MyPy instead of PyType

From my short experience with mypy:

• Good documentation 📜
• Good error surfacing
• Easy to configure
• It offers a language server, this helps with development since it integrate with IDEs

Note: removing all the type: ignore comments from the project may cause breaking changes or have a ripple effect through the entire project

Testing

Category

• slack_sdk.web.WebClient (sync/async) (Web API client)
• slack_sdk.webhook.WebhookClient (sync/async) (Incoming Webhook, response_url sender)
• slack_sdk.socket_mode (Socket Mode client)
• slack_sdk.signature (Request Signature Verifier)
• slack_sdk.oauth (OAuth Flow Utilities)
• slack_sdk.models (UI component builders)
• slack_sdk.scim (SCIM API client)
• slack_sdk.audit_logs (Audit Logs API client)
• slack_sdk.rtm_v2 (RTM client)
• /docs (Documents)
• /tutorial (PythOnBoardingBot tutorial)
• tests/integration_tests (Automated tests for this library)
• other

Requirements

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.
• I've run python3 -m venv .venv && source .venv/bin/activate && ./scripts/run_validation.sh after making the changes.

[codecov]

Codecov Report

Attention: Patch coverage is 81.87809% with 110 lines in your changes missing coverage. Please review.

Project coverage is 85.06%. Comparing base (241db14) to head (9ba8e07).

Files with missing lines	Patch %	Lines
slack_sdk/web/async_client.py	80.55%	14 Missing ⚠️
slack_sdk/web/client.py	80.55%	14 Missing ⚠️
slack_sdk/web/legacy_client.py	80.55%	14 Missing ⚠️
slack_sdk/socket_mode/builtin/internals.py	47.36%	10 Missing ⚠️
...sdk/oauth/installation_store/amazon_s3/__init__.py	36.36%	7 Missing ⚠️
slack_sdk/audit_logs/v1/logs.py	33.33%	4 Missing ⚠️
slack_sdk/web/internal_utils.py	20.00%	4 Missing ⚠️
slack_sdk/audit_logs/v1/client.py	25.00%	3 Missing ⚠️
...k_sdk/oauth/installation_store/sqlite3/__init__.py	40.00%	3 Missing ⚠️
slack_sdk/socket_mode/aiohttp/__init__.py	66.66%	3 Missing ⚠️
... and 24 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1620      +/-   ##
==========================================
+ Coverage   85.03%   85.06%   +0.03%     
==========================================
  Files         113      113              
  Lines       12661    12658       -3     
==========================================
+ Hits        10766    10768       +2     
+ Misses       1895     1890       -5     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.