bcachefs fixes for 6.12-rc5

Lots of hotfixes:
- transaction restart injection has been shaking out a few things

- fix a data corruption in the buffered write path on -ENOSPC, found by
  xfstests generic/299

- Some small show_options fixes

- Repair mismatches in inode hash type, seed: different snapshot
  versions of an inode must have the same hash/type seed, used for
  directory entries and xattrs. We were checking the hash seed, but not
  the type, and a user contributed a filesystem where the hash type on
  one inode had somehow been flipped; these fixes allow his filesystem
  to repair.

  Additionally, the hash type flip made some directory entries
  invisible, which were then recreated by userspace; so the hash check
  code now checks for duplicate non dangling dirents, and renames one of
  them if necessary.

- Don't use wait_event_interruptible() in recovery: this fixes some
  filesystems failing to mount with -ERESTARTSYS

- Workaround for kvmalloc not supporting > INT_MAX allocations, causing
  an -ENOMEM when allocating the sorted array of journal keys: this
  allows a 75 TB filesystem to mount

- Make sure bch_inode_unpacked.bi_snapshot is set in the old inode
  compat path: this alllows Marcin's filesystem (in use since before
  6.7) to repair and mount.
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