Migrate tests to Microsoft Testing Platform (MTP v2)

[Copilot]

Migrate from xUnit 2.x with VSTest to xUnit v3 with Microsoft Testing Platform v2. Update workflows for new CLI syntax.

Package changes (Directory.Packages.props)

• Removed: Microsoft.NET.Test.Sdk, xunit, xunit.analyzers, xunit.runner.visualstudio, coverlet.collector
• Added: xunit.v3.mtp-v2 3.2.0

Test project (Parlot.Tests.csproj)

• Added MTP properties: OutputType=Exe, TestingPlatformDotnetTestSupport, UseMicrosoftTestingPlatformRunner
• Suppressed xUnit1051 — tests intentionally use explicit CancellationTokens

Runtime configuration (global.json)

"test": {
  "runner": "Microsoft.Testing.Platform"
}

Workflows (build.yml, publish.yml)

# Old
run: dotnet test --configuration Release

# New (--project required with MTP)
run: dotnet test --project test/Parlot.Tests/Parlot.Tests.csproj --configuration Release

Original prompt

Migrate the tests to Microsoft Testing Platform (MTP v2). Update the github workflows with the new command line. Remove unnecessary dependencies after this change.

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