v0.4.0

test: add comprehensive tests for Matrix protocol helper functions

- Test _get_event_content() for safe content extraction
- Test _get_relation() for m.relates_to extraction
- Test _is_relation_type() for relation type checking
- Test _extract_thread_and_reply() for extracting both IDs
- Test _build_message_content() for all message types
- Test _build_edit_content() for edit messages
- Test _get_room_users() for room user extraction
- Increase test coverage and validate refactoring