feat(python): add support for persistent_memory in SessionConfig

[EaCognitive]

Problem

The GitHub Copilot SDK (Python) is currently missing support for the persistent_memory feature, which allows agents to maintain state across conversation sessions. While the underlying RPC protocol supports this, the high-level Python API does not yet expose it.

Solution

This PR adds the persistent_memory parameter to the SessionConfig TypedDict and the create_session method. The value is correctly passed through the payload to the session.create RPC call.

Changes

• python/copilot/session.py: Added persistent_memory to SessionConfig.
• python/copilot/client.py: Added persistent_memory parameter to create_session and updated the RPC payload construction.

Verification

• Added a unit test (python/test_persistent_memory_unit.py) that mocks the RPC client and verifies the persistentMemory field is correctly sent.
• Verified parity with the TypeScript SDK implementation.