Enable mypy static type checking for azure-communication-chat package

[Copilot]

Summary

This PR enables mypy static type checking for the azure-communication-chat package by setting mypy = true in the pyproject.toml configuration and fixing all resulting type errors.

Changes Made

Configuration

• pyproject.toml: Enabled mypy static type checking by changing mypy = false to mypy = true

Type Fixes

Fixed 28 mypy errors across 6 files:

Core Library Files

• _utils.py:

  • Added proper typing imports (List, Tuple, Dict, TYPE_CHECKING)
  • Fixed invalid type annotation syntax (list[(A, B)] → List[Tuple[A, B]])
  • Corrected type references (ChatThreadParticipant → ChatParticipant)
  • Added null checks to prevent returning None values in tuples

• _communication_identifier_serializer.py:

  • Fixed dictionary key assignment type issues using cast()
  • Corrected constructor calls for CommunicationUserIdentifier and UnknownIdentifier
  • Added missing import suppression for optional yarl dependency

• _chat_thread_client.py:

  • Added missing imports (ItemPaged, ChatError, CommunicationIdentifierModel)
  • Fixed return type mismatches using cast() for ItemPaged vs Iterable types
  • Corrected remove_chat_participant call to use proper model construction

• _chat_client.py:

  • Added missing imports (ItemPaged, ChatThreadItem, cast)
  • Fixed variable name collision in create_chat_thread method
  • Applied cast() for return type compatibility

Async Library Files

• aio/_chat_thread_client_async.py:

  • Fixed Optional parameter type annotations (str = None → Optional[str] = None)
  • Added missing imports and cast() for async return types
  • Fixed remove_chat_participant async call

• aio/_chat_client_async.py:

  • Fixed variable name collision in async create_chat_thread method
  • Applied cast() for AsyncItemPaged return type compatibility

Technical Details

Type Casting Strategy

Used cast() to resolve type mismatches between generated client code (returns Iterable/AsyncIterable) and public API expectations (ItemPaged/AsyncItemPaged). This is safe because the runtime objects are actually the expected paged types.

Import Organization

• Used TYPE_CHECKING imports to avoid circular dependencies
• Added proper type annotations while maintaining runtime compatibility
• Imported missing model types from generated code

Validation

✅ mypy check passes: Success: no issues found in 43 source files

The package now fully complies with mypy static type checking standards, improving type safety and developer experience for users of the azure-communication-chat SDK.

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