check: summarize findings and repairs

[charmikadi]

Description

borg check already reports individual problems as it finds them, but it was hard to tell at a glance how many issues there were overall, or how many --repair actually fixed.
This adds a short summary at the end of the check:

• for archive consistency checks, count problems found and repairs done
• for repository checks, include the error count in the finish message (repo repair still isn't implemented)
  Also updated a few repair tests to cover the new summary lines.

Fixes #2397

Checklist

• PR is against master (or maintenance branch if only applicable there)
• New code has tests and docs where appropriate
• Tests pass (run tox or the relevant test subset)
• Commit messages are clean and reference related issues

[codecov]

Codecov Report

❌ Patch coverage is 71.42857% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.22%. Comparing base (6854dca) to head (14337fe).
⚠️ Report is 4 commits behind head on master.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/borg/archive.py	69.69%	10 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #9891      +/-   ##
==========================================
- Coverage   85.24%   85.22%   -0.03%     
==========================================
  Files          93       93              
  Lines       15570    15595      +25     
  Branches     2357     2365       +8     
==========================================
+ Hits        13273    13291      +18     
- Misses       1598     1604       +6     
- Partials      699      700       +1     

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[ThomasWaldmann]

@charmikadi Thanks for helping with this!

Just be aware that @mr-raj12 is currently working on packs and that might need bigger changes in borg check also.

[ThomasWaldmann]

@mr-raj12 Check this, please.

[mr-raj12]

Thanks for working on this, @charmikadi! My repo repair PR #10048 is landing soon and it rewrites this same check() finish region in repository.py (the "repository repair not implemented" line goes away) and also ArchiveChecker.finish(), so this PR currently conflicts with master there and it's around 330 commits behind. Would suggest rebasing onto latest master and narrowing this to only the archive-side summary for now, and we can add the repository-side repairs count once #10048 is merged. I'll reuse your counting approach and credit you when I do the follow-up.