Merge branch 'ps/reftable-reflog-iteration-perf'

The code to iterate over reflogs in the reftable has been optimized
to reduce memory allocation and deallocation.

Reviewed-by: Josh Steadmon <steadmon@google.com>
cf. <Ze9eX-aaWoVaqsPP@google.com>

* ps/reftable-reflog-iteration-perf:
  refs/reftable: track last log record name via strbuf
  reftable/record: use scratch buffer when decoding records
  reftable/record: reuse message when decoding log records
  reftable/record: reuse refnames when decoding log records
  reftable/record: avoid copying author info
  reftable/record: convert old and new object IDs to arrays
  refs/reftable: reload correct stack when creating reflog iter

diff --cc refs/reftable-backend.c
Simple merge

diff --cc reftable/block.c
Simple merge

diff --cc reftable/record.c
Simple merge