feat: add ArchiveCommandHandler.Handle() tests & harden ArchiveCommandHandler

[woutervanranst]

Summary

• add reusable handler setup helpers and broaden ArchiveCommandHandler handle coverage for mixed TAR batching, deduplication, incremental, and error scenarios
• simulate upload failures via a ThrowingArchiveStorage test double and make FakeArchiveStorage extensible for overrides

Testing

• DOTNET_ROOT=$HOME/.dotnet ~/.dotnet/dotnet test src/Arius.Core.Tests/Arius.Core.Tests.csproj --filter "Category!=SkipCI" (fails: SDK 8.0.414 cannot target net9.0)

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https://chatgpt.com/codex/tasks/task_b_68edfa0cbdec8324abf154aae606064c

[codecov]

Codecov Report

❌ Patch coverage is 86.30952% with 23 lines in your changes missing coverage. Please review.
✅ Project coverage is 66.47%. Comparing base (36484da) to head (a8cf53a).
⚠️ Report is 48 commits behind head on main.

Files with missing lines	Patch %	Lines
...031145332_PointerFileEntryKeyIsOnlyRelativeName.cs	47.82%	12 Missing ⚠️
...Features/Commands/Archive/ArchiveCommandHandler.cs	89.79%	2 Missing and 3 partials ⚠️
...Features/Commands/Restore/RestoreCommandHandler.cs	69.23%	3 Missing and 1 partial ⚠️
...ateRepositories/StateRepositoryDbContextFactory.cs	50.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##            main      #82       +/-   ##
==========================================
+ Coverage   9.31%   66.47%   +57.16%     
==========================================
  Files         77       79        +2     
  Lines       3446     3535       +89     
  Branches     386      389        +3     
==========================================
+ Hits         321     2350     +2029     
+ Misses      3109     1069     -2040     
- Partials      16      116      +100     

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[github-advanced-security]

CodeQL found more than 20 potential problems in the proposed changes. Check the Files changed tab for more details.