conformance: xUnit v3 migration, config hygiene, --pull=always lint tasks

[ptr727]

Fleet CODESTYLE conformance sweep against the LanguageTags / PlexCleaner reference repos. Three items bundled into one PR.

Issue #380 — xUnit v3 + AwesomeAssertions, ILoggerFactory logging

(a) Tests on xUnit v3.

• Directory.Packages.props: replaced legacy xunit 2.9.3 with xunit.v3 3.2.2 (matching the fleet). The v3 toolchain packages (Microsoft.NET.Test.Sdk 18.7.0, coverlet.collector 10.0.1, xunit.analyzers 1.27.0, xunit.runner.visualstudio 3.1.5) and AwesomeAssertions 9.4.0 were already pinned.
• UtilitiesTests/UtilitiesTests.csproj: set IsTestProject=true and aligned package references to the PlexCleanerTests standard — xunit.v3, dropped the packaging metadata (PackageId/Version/Authors/…), SourceLink, and the now-transitive Microsoft.Extensions.Logging.Abstractions reference.
• The test suite already uses AwesomeAssertions .Should() throughout (no native Assert.* remained), so no assertion conversion was required.

(b) Library logging via ILoggerFactory. Already landed in an earlier commit on this branch — Utilities.csproj depends only on Microsoft.Extensions.Logging.Abstractions, LogOptions exposes the settable factory seam (SetFactory/TrySetFactory, defaulting to NullLoggerFactory), and Sandbox owns the concrete Serilog logger via SerilogLoggerFactory. Closing the issue here now that the xUnit half is complete.

Issue #387 — project config hygiene

• Analyzer suppressions: removed the stale CA2007 suppression from UtilitiesTests/.editorconfig; it is absent from both reference repos and the project builds warnings-clean without it under xunit.v3. The remaining suppressions were each verified still-needed by removing-and-rebuilding: CA1707/CA1515 (test project) and CA1711 (library Ex-suffix types) — all comment-justified.
• Inline pragmas: none present (grep for #pragma warning is empty).
• GlobalUsings.cs: present in every project (Utilities, UtilitiesTests, Sandbox).
• Stale package source: no GitHub Packages source exists in any nuget.config/Directory.*.props; restore is nuget.org only. Already conformant.

Fleet --pull=always

.vscode/tasks.json: inserted "--pull=always" immediately after "--rm" in each docker Lint task (editorconfig-checker, actionlint, markdownlint-cli2, cspell) so on-demand lint always pulls the :latest image. JSONC and CRLF preserved.

Validation

• dotnet build (warnings-as-errors): 0 warnings, 0 errors.
• dotnet test: 183 passed, 0 failed, 0 skipped.
• editorconfig-checker (docker :latest): clean.
• Line endings preserved per file (all edited files are CRLF; no normalization).

Closes #380
Closes #387

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 66.89%. Comparing base (f04d276) to head (97f2d85).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #403   +/-   ##
========================================
  Coverage    66.89%   66.89%           
========================================
  Files           13       13           
  Lines         1160     1160           
  Branches       108      108           
========================================
  Hits           776      776           
  Misses         338      338           
  Partials        46       46           

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[Copilot]

Pull request overview

This PR brings the Utilities repo into fleet CODESTYLE conformance by migrating the test project to xUnit v3, tightening test-project config hygiene, and ensuring VS Code Docker-based lint tasks always pull the latest images.

Changes:

• Migrate UtilitiesTests from xunit v2 to xunit.v3 (central package pin + test project references), keeping the existing AwesomeAssertions-based assertions.
• Remove a stale CA2007 suppression from the test project .editorconfig.
• Update VS Code lint tasks to run Docker with --pull=always so :latest images are refreshed on demand.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
UtilitiesTests/UtilitiesTests.csproj	Marks the project as a test project and aligns package references for xUnit v3-based test execution.
UtilitiesTests/.editorconfig	Removes a no-longer-needed analyzer suppression to keep suppressions minimal and justified.
Directory.Packages.props	Drops the legacy xUnit v2 pin and adds the xUnit v3 pin for central package management.
.vscode/tasks.json	Ensures local Docker lint tasks always pull the latest images via --pull=always.