Merge branch 'ps/reftable-fixes' into maint-2.43

Bunch of small fix-ups to the reftable code.

* ps/reftable-fixes:
  reftable/block: reuse buffer to compute record keys
  reftable/block: introduce macro to initialize `struct block_iter`
  reftable/merged: reuse buffer to compute record keys
  reftable/stack: fix use of unseeded randomness
  reftable/stack: fix stale lock when dying
  reftable/stack: reuse buffers when reloading stack
  reftable/stack: perform auto-compaction with transactional interface
  reftable/stack: verify that `reftable_stack_add()` uses auto-compaction
  reftable: handle interrupted writes
  reftable: handle interrupted reads
  reftable: wrap EXPECT macros in do/while