Remove AppVeyor

[twcclegg]

• Removes appveyor.yml, its CODEOWNERS entry, README badge, and the dead lib/update.sh
• Adds publish_nuget.yml — tag-triggered pack + push via nuget trusted publishing (OIDC, no secret)
• VersionPrefix moves from $(APPVEYOR_BUILD_VERSION) to a 0.0.0 placeholder the workflow overrides; drops the $APPVEYOR_REPO_COMMIT literal that was being written into published nuspecs
• Coverage + perf jobs move Windows → ubuntu-24.04-arm; perf workflow renamed, benchmark cache re-keyed
• netframework4.8 scoped to Windows hosts — no CI covers it any more, the main tradeoff
• System.Text.RegularExpressions scoped to net48 (NU1510 once pruning activates)
• Metadata script dispatches publish_nuget explicitly, since GITHUB_TOKEN-authored tags don't trigger workflow runs

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.01%. Comparing base (0675b76) to head (55f0744).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #368      +/-   ##
==========================================
- Coverage   98.06%   98.01%   -0.06%     
==========================================
  Files          40       39       -1     
  Lines       52975    52792     -183     
  Branches     1127     1097      -30     
==========================================
- Hits        51949    51743     -206     
- Misses        780      796      +16     
- Partials      246      253       +7     

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[wmundev]

looks good, only nit thing is that libphonenumber-csharp\csharp\PhoneNumbers.PerformanceTest\README.md has the renamed file run_performance_tests_windows.yml link in there that needs to be updated