release-24.1: kvstreamer: improve logging a bit

[blathers-crl]

Backport 1/1 commits from #124090 on behalf of @yuzefovich.

/cc @cockroachdb/release

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This commit adjusts the logging for each singleRangeBatch to include the number of scans inside of it (we only included the number of gets previously). It also drops the bitmap for whether the scans were started (this doesn't seem that useful - positions slice kinda implicitly has that information).

Additionally, it includes the TargetBytes limit that each BatchRequest was issued with into an existing log message (we have this information down at the KV level too, but it makes things easier when grepping from streamer logs specifically).

Informs: https://github.com/cockroachlabs/support/issues/2945.
Epic: None

Release note: None

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Release justification: low-risk improvement.

[blathers-crl]

Thanks for opening a backport.

Please check the backport criteria before merging:

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[blathers-crl]

It looks like your PR touches production code but doesn't add or edit any test code. Did you consider adding tests to your PR?

_{🦉 Hoot! I am a Blathers, a bot for CockroachDB. My owner is dev-inf.}

[cockroach-teamcity]

This change is 

[michae2]

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