fuse: add ACL support (Linux)

[ThomasWaldmann]

Junie (AI) experiment + some fixes the AI was not clever enough for.

But, tests fail - anyone wants to review this?

[ThomasWaldmann]

This is a bit dirty, but there is no official API call for this.

[ThomasWaldmann]

Looks like the borg mount (FUSE) process dies:

borgstore: list_start('archives', deleted=False)
borgstore: list_end('archives', deleted=False) -> 2
borgstore: load('data/f8fa64284ccde56f71d307d698a57965041516daf8af5fd7207e7688a3e7cd8d', offset=0, size=None, deleted=False) -> 342B in 0.2ms
borgstore: load('data/f8fa64284ccde56f71d307d698a57965041516daf8af5fd7207e7688a3e7cd8d', offset=0, size=None, deleted=False) -> 342B in 0.2ms
borgstore: load('data/c37fa7d38f4b2948c90981508e29b109bd792d3bfaf26473828515b5e0b6e677', offset=0, size=None, deleted=False) -> 98B in 0.2ms
borgstore: load('data/d7c1c77637a1daf247a87f5d3ab91ae241ce36211e1d63b23172993757a84254', offset=0, size=None, deleted=False) -> 246B in 0.2ms
fuse: _process_archive completed in 0.0 s for archive test
borgstore: load('data/d7c1c77637a1daf247a87f5d3ab91ae241ce36211e1d63b23172993757a84254', offset=0, size=None, deleted=False) -> 246B in 0.1ms

Calling fuse_session_destroy

borgstore: list_start('locks', deleted=False)
borgstore: list_end('locks', deleted=False) -> 1
borgstore: load('locks/a4db0b2873b82616', offset=0, size=None, deleted=False) -> 155B in 0.2ms
LOCK-RELEASE: releasing lock: {'exclusive': False, 'hostid': 'server.firma.waldmann-edv.de@57277343926478', 'processid': 2055802, 'threadid': 0, 'time': '2025-05-17T18:33:57.860+00:00', 'key': 'a4db0b2873b82616', 'dt': datetime.datetime(2025, 5, 17, 18, 33, 57, 860000, tzinfo=datetime.timezone.utc)}.
LOCK-DELETE: deleting lock from store. key: a4db0b2873b82616.
borgstore: delete('locks/a4db0b2873b82616', deleted=False) -> 0B in 0.2ms