feat: local registry timestamp

[GustavBaumgart]

Description

The timestamp of when the metric is saved is added as a second column to each per-round metric csv in the local registry.

Type of Change

• Bug Fix
• New Feature
• Breaking Change
• Refactor
• Documentation
• Other (please describe)

Checklist

• I have read the contributing guidelines
• Existing issues have been referenced (where applicable)
• I have verified this change is not present in other open pull requests
• Functionality is documented
• All code style checks pass
• New code contribution is covered by automated tests
• All new and existing tests pass

[codecov-commenter]

Codecov Report

Merging #426 (5f3b035) into main (5abf5f6) will not change coverage.
The diff coverage is n/a.

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  Coverage   14.86%   14.86%           
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  Files          48       48           
  Lines        2832     2832           
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  Hits          421      421           
  Misses       2382     2382           
  Partials       29       29