feat(sessions): add get_events() and filter_events() methods to Session

[ecanlar]

Summary

This PR implements event filtering capabilities for the Session class to support rewind operations.

Changes

• Added get_events() method: Provides a consistent API for accessing all session events
• Added filter_events() method: Allows filtering events with options to exclude rewound events
• Implemented rewind filtering logic: When a session is rewound, events from the rewound invocation onwards are automatically filtered out
• Comprehensive test coverage: Added extensive unit tests covering all scenarios including edge cases

Key Features

1. get_events(): Returns all events in the session
2. filter_events(exclude_rewound=True): Returns filtered events, excluding those invalidated by rewind operations
3. Backward iteration algorithm: Efficiently filters rewound events by iterating backward through the event list

Testing

The implementation includes comprehensive unit tests in test_session_filter_events.py covering:

• Normal event retrieval
• Single and multiple rewind scenarios
• Edge cases (rewind target not found, chronological order preservation)
• Multiple events in the same invocation

Files Changed

• src/google/adk/sessions/session.py - Added get_events() and filter_events() methods with rewind filtering logic
• tests/unittests/sessions/test_session_filter_events.py - Comprehensive unit tests

Related Issue

Fixes #4959

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[rohityan]

Hi @ecanlar , Thank you for your contribution! We appreciate you taking the time to submit this pull request. Can you please fix the formatting errrors. You can use autoformat.sh

[ecanlar]

Hi @rohityan, formatting errors are fixed by running autoformat.sh. The code now follows the Google Python Style Guide with proper indentation (2 spaces) and import ordering.

[ecanlar]

I've just pushed a commit that adds full support for nested Pydantic models!
The implementation is based on ADK's existing _resolve_references() function in openapi_spec_parser.py, which already handles similar reference resolution for OpenAPI tools. I adapted it for Pydantic's specific schema structure.