fix: Enhance error handling in PgCheckpointer and update thread name …

[Iamsdt]

This pull request updates the PgCheckpointer's thread storage logic to provide clearer feedback on whether a thread was newly created or updated, and improves error handling. It also adds new tests to ensure the correct behavior of these changes.

Enhancements to thread storage and update logic:

• The aput_thread method now returns a boolean indicating if a thread was newly created (True) or if an existing thread was updated (False). The logic first attempts to insert, and if the thread already exists, it updates only the necessary fields, defaulting to the existing thread name if none is provided. [1] [2] [3]

Improved error handling:

• Exception handling in both aput_thread and _get_thread now consistently raises the original exception object for better traceability. [1] [2]

Testing and documentation:

• New and updated tests verify the new return value of aput_thread and its behavior on both insert and update paths.
• The changelog has been updated to document these improvements and clarify the new behavior.

[codecov]

Codecov Report

❌ Patch coverage is 69.23077% with 4 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
agentflow/checkpointer/pg_checkpointer.py	69.23%	3 Missing and 1 partial ⚠️

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