check: --max-age and --max-duration cover the archives check, fixes #10025

[mr-raj12]

Description

Fixes #10025, refs #10356. Implements what was agreed in #10025 (comment).

borg check now records the result of the archives check per archive in cache/checked-archives (archive id -> timestamp, result), in the same format and envelope as cache/checked-packs.

• --max-age also skips archives whose ok record is younger than the timespan, and is allowed with --archives-only. --repair and --verify-data check every archive.
• --max-duration is one time budget for the repository check and the archives check, and no longer requires --repository-only. The archives check takes the archives without an ok record first, then the least recently checked ones, and stops between two archives after it analyzed at least one.
• All archive records are cleared when a check finds a corrupt or missing pack or salvages a pack, and when the archives check runs with --repair.

Commits:

1. repository: split CheckTracker out of PackTracker: refactoring only, no behavior change.
2. check: --max-age and --max-duration cover the archives check: the feature, tests and docs.

Decisions that go beyond the issue discussion, please object if you disagree:

• An archives check stores and reuses no archive records while a pack is recorded corrupt in checked-packs, and when a run without --repair has a finding before it analyzes the archives (missing pack, dropped content, --verify-data or --find-lost-archives error).
• If the repository check uses up --max-duration, the archives check is skipped with an info message. Without --max-age, a repository check that never finishes within the budget therefore never lets the archives check run. The help text says so and suggests --max-age or separate --repository-only / --archives-only runs.
• Like a pack recorded corrupt, an archive recorded with a problem fails a partial archives check that does not get to it.
• An archives check that starts analyzes at least one archive even if the budget is already used up, as the repository check verifies at least one pack. So --archives-only --max-duration makes progress in every run.
• --max-duration is rejected with --verify-data and --find-lost-archives, as both scan the whole repository.
• A client without write permission for cache/ (BORG_REPO_PERMISSIONS=read-only) can still run check --archives-only, it logs a warning and stores no records.

Timing, 10 archives of 100k files each, aes256-ocb, local repository:

command	time
check --archives-only	12.2s
check --archives-only --max-age=1d	1.1s
check --max-age=1d	1.2s
check --repository-only	1.1s
check --archives-only --max-duration=3	4.5s, 3 of 10 archives analyzed

docs/changes.rst and the generated usage docs are not touched. This touches the same files as #10194 and #9891, I will rebase when needed.

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 97.43590% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.13%. Comparing base (7e3d305) to head (f89809b).
⚠️ Report is 7 commits behind head on master.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/borg/repository.py	93.61%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #10504      +/-   ##
==========================================
+ Coverage   89.12%   89.13%   +0.01%     
==========================================
  Files         103      103              
  Lines       19783    19868      +85     
  Branches     3099     3115      +16     
==========================================
+ Hits        17631    17710      +79     
- Misses       1490     1497       +7     
+ Partials      662      661       -1     

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