Fix/stream

[Iamsdt]

This pull request introduces several improvements and refactors to both the streaming React agent example and the PostgreSQL checkpointer implementation. The key changes focus on adding flexible synchronous and asynchronous streaming test modes, improving logging and debugging, and making the PostgreSQL connection pool initialization lazy for better resource management.

Streaming agent and test improvements:

• Added multiple entry points to stream_react_agent.py for running streaming, non-streaming, synchronous, and synchronous streaming tests, allowing easier testing of agent modes from the command line.
• Refactored agent logic to support both async and sync execution, including new main_agent_sync, main_agent_sync_stream, and main_agent_non_stream implementations, and corresponding graph setups for each test type. [1] [2]
• Improved logging and debugging by initializing the logger and printing registered tools for easier troubleshooting. [1] [2] [3]

PostgreSQL checkpointer enhancements:

• Changed PostgreSQL pool initialization to be lazy, storing configuration and only creating the pool when first needed; updated all relevant methods to use the lazy pool getter. [1] [2] [3] [4] [5] [6] [7] [8]
• Improved state serialization to handle Enum types correctly, ensuring compatibility with JSON storage.

Documentation update:

• Removed the TESTING.md file, which previously described test setup and organization for the PyAgenity library.