Add RegistryExtensions with ContainsSubKey

[Copilot]

Ports RegistryExtensions from DotnetRuntimeBootstrapper into PowerKit.

• RegistryExtensions.ContainsSubKey(string name) — extends RegistryKey; returns true if a sub-key with the given name can be opened. Marked [SupportedOSPlatform("windows")] on all active TFMs to satisfy CA1416. Opens and immediately disposes the sub-key to avoid a resource leak. Guarded with #if NET5_0_OR_GREATER || NETFRAMEWORK so the extension is available on both .NET 5+ and classic .NET Framework; the outer guard also ensures the source file compiles cleanly when PowerKit.csproj targets netstandard2.0 without any extra package reference. SupportedOSPlatformAttribute is polyfilled by PolyShim on non-NET5+ TFMs (including NETFRAMEWORK), so no custom polyfill is needed.
• RegistryExtensionsTests — two tests (key exists / key does not exist); use [SkippableFact] + Skip.IfNot(OperatingSystem.IsWindows()) so tests are properly reported as skipped on non-Windows CI.

using var key = Registry.LocalMachine.OpenSubKey(@"SOFTWARE\Microsoft", false)!;
key.ContainsSubKey("Windows"); // true
key.ContainsSubKey("nonexistent-key"); // false

[Tyrrrz]

@copilot use SkippableFact to skip tests

[Tyrrrz]

@copilot please fix the build

[Copilot]

@copilot use SkippableFact to skip tests

Done in 083597c. Added xunit.skippablefact 1.5.61 and switched to [SkippableFact] + Skip.IfNot(OperatingSystem.IsWindows()). Tests now show as properly skipped on Linux instead of silently passing.

[Copilot]

@copilot please fix the build

Fixed in 3d89f99. PowerKit targets netstandard2.0 where RegistryKey isn't in the BCL — added Microsoft.Win32.Registry 5.0.0 as a package reference to PowerKit.csproj and Directory.Packages.props. Build now succeeds with 0 errors.

[Copilot]

Pull request overview

Ports a Windows Registry helper into PowerKit by introducing a RegistryKey extension that checks for the presence of a sub-key, along with tests to validate the behavior.

Changes:

• Add RegistryExtensions.ContainsSubKey(string name) for Microsoft.Win32.RegistryKey.
• Add xUnit tests covering the “exists” and “does not exist” cases (guarded for Windows).

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 5 comments.

File	Description
PowerKit/Extensions/RegistryExtensions.cs	Adds a RegistryKey extension method to check whether a sub-key can be opened.
PowerKit.Tests/RegistryExtensionsTests.cs	Adds tests for the new extension method with a Windows-only runtime guard.

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[Tyrrrz]

@copilot resolve the merge conflicts in this pull request

[Copilot]

@copilot resolve the merge conflicts in this pull request

Done in b9d913e. Merged origin/prime — the only conflicts were in Directory.Packages.props and PowerKit.Tests.csproj over the package name casing (xunit.skippablefact → Xunit.SkippableFact). Resolved by taking the prime casing. All 121 tests pass.

[Copilot]

@copilot resolve the merge conflicts in this pull request

Done in f318c6c. Merged origin/prime — the only change was adding PrivateAssets="all" to the PolyShim package reference. No conflicts; all 121 tests pass.

[Tyrrrz]

@copilot no, I meant that it should already be polyfilled by PolyShim

[Copilot]

@copilot no, I meant that it should already be polyfilled by PolyShim

Done in 86964ec. Removed the custom polyfill file — PolyShim's SupportedOSPlatformAttribute.cs already has #if (NETCOREAPP && !NET5_0_OR_GREATER) || (NETFRAMEWORK) || (NETSTANDARD), covering NETFRAMEWORK. The [SupportedOSPlatform("windows")] in RegistryExtensions.cs remains unconditional.