reftable/record: reuse refnames when decoding log records
When decoding a log record we always reallocate their refname arrays.
This results in quite a lot of needless allocation churn.
Refactor the code to grow the array as required only. Like this, we
should usually only end up reallocating the array a small handful of
times when iterating over many refs. Before:
HEAP SUMMARY:
in use at exit: 13,473 bytes in 122 blocks
total heap usage: 4,068,487 allocs, 4,068,365 frees, 332,011,793 bytes allocated
After:
HEAP SUMMARY:
in use at exit: 13,473 bytes in 122 blocks
total heap usage: 3,068,488 allocs, 3,068,366 frees, 307,122,961 bytes allocated
Signed-off-by: Patrick Steinhardt <ps@pks.im> Signed-off-by: Junio C Hamano <gitster@pobox.com>