Merge branch 'ps/reftable-binsearch-updates'

Merge branch 'ps/reftable-binsearch-updates'

Reftable code clean-up and some bugfixes.

* ps/reftable-binsearch-updates:
  reftable/block: avoid decoding keys when searching restart points
  reftable/record: extract function to decode key lengths
  reftable/block: fix error handling when searching restart points
  reftable/block: refactor binary search over restart points
  reftable/refname: refactor binary search over refnames
  reftable/basics: improve `binsearch()` test
  reftable/basics: fix return type of `binsearch()` to be `size_t`