Add LockFile

[Copilot]

Ports LockFile from Onova into PowerKit as a general-purpose utility.

Changes

• PowerKit/LockFile.cs — file-based exclusive lock; TryAcquire opens the file with FileShare.None and returns null on IOException (the exception .NET raises when the file is already held)
• PowerKit.Tests/LockFileTests.cs — covers successful acquisition, blocked re-acquisition while held, and re-acquisition after disposal

Usage

using var lockFile = LockFile.TryAcquire("/path/to/lock");
if (lockFile is null)
{
    // another process holds the lock
}

[Copilot]

Pull request overview

This PR ports Onova’s LockFile helper into PowerKit, adding a small file-based exclusive lock primitive plus tests to validate acquisition and release behavior.

Changes:

• Added LockFile utility with TryAcquire(path) semantics.
• Added unit tests covering acquisition, contention, and reacquisition after disposal.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
PowerKit/LockFile.cs	Introduces the file-based locking utility and acquisition API.
PowerKit.Tests/LockFileTests.cs	Adds tests validating basic lock acquisition/contended acquisition/disposal behavior.

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