[BUG] OBO between log service and compaction.

[rescrv]

Compaction assumes that enumeration position t_i means t_i was the last
record seen and therefore next reader should read from t_i + 1.

Log service was built and tested for t_i meaning t_i was the first
record to return.

Somehow it passed tests, so let's see if this one does.

Note: I changed the go code, but only by moving a +1 out a layer. The
inner version was inconsistent with convention, so I updated it.

[github-actions]

Reviewer Checklist

Please leverage this checklist to ensure your code review is thorough before approving

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?
• Can you think of any inputs or external events that could break the code? Is user input validated and safe? Have they been tested?
• If appropriate, are there adequate property based tests?
• If appropriate, are there adequate unit tests?
• Should any logging, debugging, tracing information be added or removed?
• Are error messages user-friendly?
• Have all documentation changes needed been made?
• Have all non-obvious changes been commented?

System Compatibility

• Are there any potential impacts on other parts of the system or backward compatibility?
• Does this change intersect with any items on our roadmap, and if so, is there a plan for fitting them together?

Quality

• Is this code of a unexpectedly high quality (Readability, Modularity, Intuitiveness)