More bcachefs bugfixes for 6.7

Bigger/user visible fixes:

 - bcache & bcachefs were broken with CFI enabled; patch for closures to
   fix type punning

 - mark erasure coding as extra-experimental; there are incompatible
   disk space accounting changes coming for erasure coding, and I'm
   still seeing checksum errors in some tests

 - several fixes for durability-related issues (durability is a device
   specific setting where we can tell bcachefs that data on a given
   device should be counted as replicated x times )

 - a fix for a rare livelock when a btree node merge then updates a
   parent node that is almost full

 - fix a race in the device removal path, where dropping a pointer in a
   btree node to a device would be clobbered by an in flight btree write
   updating the btree node key on completion

 - fix one SRCU lock hold time warning in the btree gc code - ther's
   still a bunch more of these to fix

 - fix a rare race where we'd start copygc before initializing the "are
   we rw" percpu refcount; copygc would think we were already ro and die
   immediately

https://evilpiepirate.org/~testdashboard/ci?branch=bcachefs-for-upstream
-----BEGIN PGP SIGNATURE-----
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=vN+y
-----END PGP SIGNATURE-----