Add ProgressMuxer and DelegateProgress utilities

[Copilot]

Ports ProgressMuxer from Onova into PowerKit as a source-only utility. Combines weighted IProgress<double> inputs into a single aggregated output.

Changes

• PowerKit/ProgressMuxer.cs — core implementation

  • Guarded with #if NET40_OR_GREATER || NETSTANDARD || NET (IProgress<T> unavailable on net35)
  • Uses System.Threading.Lock and EnterScope() (polyfilled by PolyShim 2.10.0 for all pre-.NET 9 targets)
  • Uses Interlocked.Increment for thread-safe input index allocation in CreateInput
  • Returns a DelegateProgress<double> from CreateInput rather than Progress<T>, which avoids async dispatch via SynchronizationContext

• PowerKit/DelegateProgress.cs — new standalone utility type

  • internal sealed class DelegateProgress<T> : IProgress<T> that delegates reporting to an Action<T>
  • Guarded with #if NET40_OR_GREATER || NETSTANDARD || NET
  • Usable independently of ProgressMuxer

• PowerKit.Tests/ProgressMuxerTests.cs — covers single input, weighted input, and multiple weighted inputs

Usage

var muxer = new ProgressMuxer(outputProgress);

var downloadProgress = muxer.CreateInput(weight: 0.7);
var extractProgress  = muxer.CreateInput(weight: 0.3);

// Each input contributes proportionally to the combined output
downloadProgress.Report(1.0); // output sees 0.7
extractProgress.Report(1.0);  // output sees 1.0

DelegateProgress<T> can also be used standalone:

IProgress<double> progress = new DelegateProgress<double>(p => Console.WriteLine(p));
progress.Report(0.5); // prints 0.5

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.56%. Comparing base (e1aaff9) to head (a7b0e90).
⚠️ Report is 5 commits behind head on prime.

Additional details and impacted files

@@            Coverage Diff             @@
##            prime      #48      +/-   ##
==========================================
+ Coverage   94.36%   94.56%   +0.19%     
==========================================
  Files          82       92      +10     
  Lines        1740     1951     +211     
  Branches      141      152      +11     
==========================================
+ Hits         1642     1845     +203     
- Misses         72       77       +5     
- Partials       26       29       +3     

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[Copilot]

Pull request overview

Adds a new source-only utility (ProgressMuxer) to aggregate multiple weighted IProgress<double> inputs into a single output progress reporter, along with tests validating basic aggregation behavior.

Changes:

• Added ProgressMuxer implementation that combines multiple weighted progress inputs into one output.
• Added unit tests for single input, weighted input, and multiple weighted inputs.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

File	Description
PowerKit/ProgressMuxer.cs	Introduces ProgressMuxer + internal delegate-based IProgress<double> input implementation.
PowerKit.Tests/ProgressMuxerTests.cs	Adds coverage for aggregation behavior across different input/weight scenarios.

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