fix: backport error handling fixes to existing connectors

[hallvictoria]

Summary

Comprehensive error handling improvements across 14 connector clients with +205 new tests, source bug fixes, and code quality improvements.

Fixes #38, #39

Changes

Fixed

• outlook.py & office365.py: Fixed variable shadowing in respond_to_event_async methods (mypy error)
• teams.py: Fixed incorrect ConnectorException signature in 2 webhook methods (used keyword args instead of positional)
• test_arm.py: Fixed 3 test failures (wrong URL assertion, incorrect method parameters)

Changed

• 14 connector source files: Regenerated with SDK Generator fixes
• 15 test files: Added error handling tests for HTTP 4xx/5xx responses
• test_code_quality.py: Added flake8 and mypy validation tests

Updated

• README.md — Updated test counts for 14 connectors (+205 tests total)
• CHANGELOG.md — Documented changes under [Unreleased]

Testing

• Unit tests added/updated
• All existing tests pass (pytest)
• Linting passes (flake8 src/ tests/)
• Manual testing (describe below if applicable)

Checklist

• Code follows the project's coding conventions
• No modifications to generated connector files in src/azure/connectors/*.py (unless regenerated)
• Type hints added to all public API signatures
• Documentation updated (if behavior changed)
• CHANGELOG.md updated (if user-facing change)