Separate unread and read stats and logging files and avoid a circular rename

[adamnovak]

This might fix #1727 by definitively moving stats and logging files from a stats/inbox directory to a stats/archive directory when the leader processes them. It no longer renames them back to the .new suffix they had when they were being written, which avoids trying to directly undo a rename that just happened from another node, which is a thing that a very broken filesystem might find confusing.

This also means we don't need to scan through all previously-processed stats and logging files to find new ones; we only have to scan stats/inbox.

Changelog Entry

To be copied to the draft changelog by merger:

• Organize stats and logging files into stats/inbox and stats/archive and avoid a circular rename.

Reviewer Checklist

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    contrib/admin/test-pr otheruser theirbranchname issues/XXXX-fix-the-thing
    

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Merger Checklist

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• Copy its recommended changelog entry to the Draft Changelog.
• Append the issue number in parentheses to the changelog entry.

[stxue1]

Looks pretty good to me