- Replaces the explicit media event tuple with MATRIX_MEDIA_EVENT_FILTER
based on
media base classes: (RoomMessageMedia, RoomEncryptedMedia).
- Keeps MatrixMediaEvent as the static typing alias for media-specific
handlers.
- Removes MatrixInboundEvent and uses RoomMessage in mention-related
logic.
- Adds regression tests for:
- callback registration using MATRIX_MEDIA_EVENT_FILTER
- ensuring RoomMessageText is not matched by the media filter.