this largely sorts out contention when using poudriere
```
commit f5b821a6f60f688c0e065a5265bbbc0ac186f3d8
Author: Mateusz Guzik <mjg@FreeBSD.org>
Date: Wed Oct 1 10:06:39 2025 +0000
nullfs: avoid the interlock in null_lock with smr
This largely eliminates contention on the vnode interlock.
Note this still does not scale, to be fixed(tm).
commit f87cf08714fa72b4d2acaf705ffce24db09b923f
Author: Mateusz Guzik <mjg@FreeBSD.org>
Date: Tue Sep 30 15:16:30 2025 +0000
nullfs: smr-protected hash lookup
Vast majority of real-world contention on the hash comes from lookups,
notably seen during highly parallel poudriere runs.
Lockless lookup largely alleviates the problem.
Tested by: pho (previous version)
commit 574060ec8839752d628c6003821afdbb62466a4a
Author: Mateusz Guzik <mjg@FreeBSD.org>
Date: Wed Oct 1 10:28:48 2025 +0000
nullfs: assert the vnode is not doomed in null_hashget_locked
While here some style touch ups and fixing a stale name in an assert.
```