417e28f941
Rewrite mock infrastructure across three test files: - test_matrix.py: replace fake nio module with fake mautrix module tree, update all client method mocks to new API names and return types - test_matrix_voice.py: update event construction, download/upload mocks, handler invocation (single event arg, no room object) - test_matrix_mention.py: update mock module, event construction, DM detection via _dm_rooms cache instead of room.member_count 157 tests passing.