gvfs-udisks2-volume-monitor still has high cpu usage

I'm running microk8s locally on my developer machine and the deployments create a bunch of mounts:

$ mount | wc -l
642

Most of these shouldn't be interesting to the volume monitor:

$ mount | grep microk8s | wc -l
510

However, even when these mounts are excluded (e.g. with the x-gvfs-hide mount option), CPU usage of the volume-monitor is still unacceptably high (constant ~90% CPU usage). I've backported the fix from #713 (closed) (I'm on Ubuntu 24.04) but I'm still seeing high CPU usage.

Recording the process with sudo perf record -p <pid> gives the following report (excerpt):

# Samples: 82  of event 'cpu_atom/cycles/P'
# Event count (approx.): 3006878784
#
# Children      Self       Samples  Command          Shared Object                Symbol                             
# ........  ........  ............  ...............  ...........................  ...................................
#
    99.04%     0.00%             0  gvfs-udisks2-vo  gvfs-udisks2-volume-monitor  [.] should_include_volume
            |
            ---should_include_volume
               g_unix_mount_at
               |          
               |--87.10%--0x735301978d2e
               |          |          
               |          |--79.85%--0x735301490c76
               |          |          mnt_table_parse_file
               |          |          |          
               |          |          |--64.03%--mnt_table_parse_stream
               |          |          |          |          
               |          |          |          |--45.00%--__getdelim
               |          |          |          |          |          
               |          |          |          |          |--43.96%--_IO_file_underflow@@GLIBC_2.2.5
               |          |          |          |          |          read

The problem is should_include_volume_check_mount_points calls g_unix_mount_at in a loop for each mount, and g_unix_mount_at parses the mount table and does string comparisons on each row to find the correct mount, which burns a lot of CPU.

I think the improvement for this is fairly trivial, get all mounts once with g_unix_mounts_get and reference those instead.

I'll raise a PR, but this is my first contribution to a GNOME project (and my first contribution in C for 20 years), so please do point me at anything I've missed.