[BUG] Fix an ordering and windowing bug in new log service.

[rescrv]

This fixes a critical bug in the as-of-yet-unreleased log service in
which logs would pull incorrectly. The flow of the bug is as follows:

1. Fetch logs scans to get a Vec.
2. Fetch all parquet files in parallel.
3. Take the first batch_size records across all files regardless of
   their start/limit.

[github-actions]

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Testing, Bugs, Errors, Logs, Documentation

• Can you think of any use case in which the code does not behave as intended? Have they been tested?
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• If appropriate, are there adequate property based tests?
• If appropriate, are there adequate unit tests?
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Quality

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