release-22.1: cfetcher: correctly update the limit hint

[yuzefovich]

Backport 1/1 commits from #88391.

/cc @cockroachdb/release

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In 41fa8b6 (which was supposed to be a "noop" refactor) we introduced a bug which made it so that we no longer update the remaining limit hint correctly. As a result, the cFetcher might no longer respect the limit hint. What makes things worse is the fact that the KV layer still does everything correctly, so when the cFetcher asks for more rows that exceed the limit, the KV layer does a BatchRequest with 10x of the original limit. This is now fixed by correctly updating the limit hint right before emitting the batch.

Addresses: #88382.

Release note (bug fix): CockroachDB no longer fetches unnecessary rows for queries with LIMITs. The bug was introduced in 22.1.7.

Release justification: bug fix.

[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 

[DrewKimball]

Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @mgartner)