Python: sessions: Add get_new_session, get_session_by_id methods #3588
Description
Add helper methods for session/thread management:
- get_new_session() - should not have side-effects like chat history provider being called
- get_session_by_id(id)
- get_session_from_history(history)
File: python/packages/core/agent_framework/_threads.py
Location: Line ~310
Action: Implement these session management helper methods.
Parent issue: #3575