release-24.2.1-rc: release-24.2: storage: fix comparison of suffixes

[blathers-crl]

Backport 1/1 commits from #129605 on behalf of @RaduBerinde.

/cc @cockroachdb/release

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This is a partial backport of #128043. CC @cockroachdb/release

Release justification: this fixes an issue hit in a real cluster where
a range key is never cleaned up.

The EngineComparer has a bug when comparing bare suffixes - we call
the normalization function on a slice without the sentinel byte; that
function's logic is based on length so it will not function properly.

We recently observed that this can cause problems when a
RangeKeySet has a suffix with the (now obsolete) synthetic bit set,
and the corresponding RangeKeyUnset is issued by a newer version and
doesn't have the bit set. These suffixes are supposed to equal each
other but this is not currently the case.

We fix the comparator to account for this case correctly and add a
more comprehensive test. On the old code, the updated test failed
with:

Compare(0000000000000002000000010d, 000000000000000200000001010e) = 1, expected 0

Fixes: #129592
Release note: None

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Release justification:

[blathers-crl]

Thanks for opening a backport.

Please check the backport criteria before merging:

• Backports should only be created for serious
  issues or test-only changes.
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[cockroach-teamcity]

This change is