release-24.2: storage: fix comparison of suffixes

[RaduBerinde]

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

[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.
• Backports should not break backwards-compatibility.
• Backports should change as little code as possible.
• Backports should not change on-disk formats or node communication protocols.
• Backports should not add new functionality (except as defined
  here).
• Backports must not add, edit, or otherwise modify cluster versions; or add version gates.
• All backports must be reviewed by the owning areas TL. For more information as to how that review should be conducted, please consult the backport
  policy.

If your backport adds new functionality, please ensure that the following additional criteria are satisfied:

• There is a high priority need for the functionality that cannot wait until the next release and is difficult to address in another way.
• The new functionality is additive-only and only runs for clusters which have specifically “opted in” to it (e.g. by a cluster setting).
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Also, please add a brief release justification to the body of your PR to justify this
backport.

[cockroach-teamcity]

This change is 

[nicktrav]

Note: once this lands, if we can, we'll want to cherry-pick this onto release-24.2.1-rc too (I shall request that branch be unfrozen).

[jbowens]

Reviewed 2 of 2 files at r1, all commit messages.
Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @nicktrav, @RaduBerinde, and @tbg)

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pkg/storage/pebble.go line 499 at r1 (raw file):

		panic(errors.AssertionFailedf("malformed suffix: %x", a))
	}
	// Strip off sentinel byte.

nit: "sentinel byte" is confusing. the sentinel byte is the 0x00 byte at the end of prefix, whereas this is the version-length byte we're trimming.

[RaduBerinde]

Reviewable status: complete! 0 of 0 LGTMs obtained (and 1 stale) (waiting on @jbowens, @nicktrav, and @tbg)

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pkg/storage/pebble.go line 499 at r1 (raw file):

Previously, jbowens (Jackson Owens) wrote…

nit: "sentinel byte" is confusing. the sentinel byte is the 0x00 byte at the end of prefix, whereas this is the version-length byte we're trimming.

Yeah, I keep confusing the terminology, fixed.

[blathers-crl]

Based on the specified backports for this PR, I applied new labels to the following linked issue(s). Please adjust the labels as needed to match the branches actually affected by the issue(s), including adding any known older branches.

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Issue #129592: branch-release-23.1, branch-release-23.2, branch-release-24.2.1-rc.

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[blathers-crl]

Encountered an error creating backports. Some common things that can go wrong:

1. The backport branch might have already existed.
2. There was a merge conflict.
3. The backport branch contained merge commits.

You might need to create your backport manually using the backport tool.

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error creating merge commit from 5daa9f6 to blathers/backport-release-23.1-129605: POST https://api.github.com/repos/cockroachdb/cockroach/merges: 409 Merge conflict []

you may need to manually resolve merge conflicts with the backport tool.

Backport to branch 23.1.x failed. See errors above.

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