release-23.2: streamingccl: use correct bounds for range key SSTs

[blathers-crl]

Backport 1/1 commits from #112903 on behalf of @stevendanna.

/cc @cockroachdb/release

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Previously, we were erroneously calling Next() on the end key of our SST even though the end key already represented an exclusive bounds.

This Next() meant that the bounds of our SSTs were slightly incorrect. In most cases, this was harmless, but in the case of a range boundary that aligned directly with the actual bounds of the SST, it could result in us attempting to split an SST into 2 with the RHS ending up empty.

Here, we fix that and also make our SST splitting a bit more robust to bad input. It now errors if the LHS or RHS ends up empty despite a split key inside the given bounds. It also handles split keys outside of the bounds. Neither of these things should happen unless our contract with other parts of the system changes.

Fixes #112846

Release note (bug fix): Fix a bug that could prevent phyiscal replication from advancing in the face of some range deletion operations.

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Release justification: Low risk bug fix for a critical bug in physical replication.

[blathers-crl]

Thanks for opening a backport.

Please check the backport criteria before merging:

• Patches should only be created for serious issues or test-only changes.
• Patches should not break backwards-compatibility.
• Patches should change as little code as possible.
• Patches should not change on-disk formats or node communication protocols.
• Patches should not add new functionality.
• Patches must not add, edit, or otherwise modify cluster versions; or add version gates.

If some of the basic criteria cannot be satisfied, ensure that the exceptional criteria are satisfied within.

• 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).
• New code is protected by a conditional check that is trivial to verify and ensures that it only runs for opt-in clusters.
• The PM and TL on the team that owns the changed code have signed off that the change obeys the above rules.

Add a brief release justification to the body of your PR to justify this backport.

Some other things to consider:

• What did we do to ensure that a user that doesn’t know & care about this backport, has no idea that it happened?
• Will this work in a cluster of mixed patch versions? Did we test that?
• If a user upgrades a patch version, uses this feature, and then downgrades, what happens?

[cockroach-teamcity]

This change is 

[stevendanna]

bors r=dt

[craig]

👎 Rejected by label