feat: Implement chat history API for Azure AI Foundry (#142)

* feat: Implement chat history API for Azure AI Foundry

- Added `send_chat_history_messages` and `send_chat_history` methods to handle chat history messaging.
- Introduced message conversion logic to transform ThreadMessage objects into ChatHistoryMessage format.
- Implemented input validation for method parameters.
- Created unit tests for input validation, message conversion, success paths, error handling, and edge cases.
- Added mock classes for testing Azure AI Foundry message structures.
- Established shared pytest fixtures for consistent testing setup.

* Update docs/prd/azure-ai-foundry-chat-history-api-tasks.md

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Update tests/tooling/extensions/azureaifoundry/services/test_send_chat_history.py

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* refactor: Ensure core service is called even for empty message lists in send_chat_history

---------

Co-authored-by: Johan Broberg <johanb@microsoft.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: 3 people