Investigate what causes LXD's dqlite to create lots of singleton closed segments

[cole-miller]

See these reports:

• https://discourse.ubuntu.com/t/lxd-5-21-1-lts-has-been-released/43823/49
• https://discourse.ubuntu.com/t/lxd-5-0-3-on-ubuntu-22-04-stopped-working-with-lxc-ls-returning-error-get-http-unix-socket-1-0-eof/42412/10

I don't know whether this is causally related to the "closed segment past last snapshot" condition or not; it could be happening in lots of other cases in the wild without us ever seeing it.