fusefs: implement attribute cache timeouts

The FUSE protocol allows the server to specify the timeout period for the
client's attribute and entry caches. This commit implements the timeout
period for the attribute cache. The entry cache's timeout period is
currently disabled because it panics, and is guarded by the
vfs.fusefs.lookup_cache_expire sysctl.

PR: 235773
Reported by: cem
Sponsored by: The FreeBSD Foundation