Finalising all rsyncers through the instrument server seems to cause connection issues with the database

The first error log:

`sqlalchemy.exc.OperationalError: (psycopg2.OperationalError) server closed the connection unexpectedly
This probably means the server terminated abnormally
before or while processing the request.

[SQL: SELECT session.id, session.name, session.visit, session.started, session.current_gain_ref, session.instrument_name
FROM session
WHERE session.id = %(id_1)s]
[parameters: {'id_1': 22}]
(Background on this error at: https://sqlalche.me/e/20/e3q8)`

occurring in `validate_instrument_server_session_token` in auth.

The rsyncer finalisatons happen outside of threads (https://github.com/DiamondLightSource/python-murfey/blob/7e412424845eda96abed07165b781f433cc6ad56/src/murfey/client/multigrid_control.py#L169) which may cause issues