Make Disposable.Create produce idempotent disposables

[Copilot]

Disposable.Create previously returned a disposable that invoked the delegate on every Dispose() call. The produced disposable should only invoke the action once, regardless of how many times it is disposed.

Changes

• DelegateDisposable: uses Interlocked.Exchange on an int flag to ensure the delegate fires exactly once, with thread-safety guarantees
• DisposableTests: adds Create_Idempotent_Test asserting that repeated Dispose() calls invoke the action only once

var count = 0;
var disposable = Disposable.Create(() => Interlocked.Increment(ref count));

disposable.Dispose();
disposable.Dispose();
disposable.Dispose();

count == 1; // true

[Tyrrrz]

@copilot let's mention the idempotency in remarks in xmldocs

[Copilot]

Pull request overview

This PR changes Disposable.Create to return an idempotent IDisposable, ensuring the provided delegate is invoked at most once even if Dispose() is called multiple times (including from multiple threads).

Changes:

• Updated the internal DelegateDisposable to gate invocation with an Interlocked flag so disposal happens exactly once.
• Added a new unit test verifying that repeated Dispose() calls only invoke the action once.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
PowerKit/Disposable.cs	Makes Disposable.Create-backed disposables idempotent via an Interlocked-guarded DelegateDisposable.
PowerKit.Tests/DisposableTests.cs	Adds a regression test asserting multiple Dispose() calls only trigger the action once.

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[Copilot]

@copilot let's mention the idempotency in remarks in xmldocs

Updated in 1c28146 — Disposable.Create now documents idempotency in XML docs remarks.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.52%. Comparing base (6ff6600) to head (b390b2f).

Additional details and impacted files

@@           Coverage Diff           @@
##            prime      #95   +/-   ##
=======================================
  Coverage   86.51%   86.52%           
=======================================
  Files          78       78           
  Lines        1409     1410    +1     
  Branches      242      243    +1     
=======================================
+ Hits         1219     1220    +1     
  Misses        137      137           
  Partials       53       53           

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