Avoid unlimited-loop spin when rendering is skipped

[SteffenCarlsen]

Fixes FrameRateLimit.Unlimited so paused, hidden, or target-paused overlays report skipped work and the owner thread briefly waits instead of spinning hot. Active unlimited rendering still runs without the fixed frame delay. Validation: dotnet test tests\ModernOverlay.Tests\ModernOverlay.Tests.csproj --configuration Debug --filter HiddenUnlimitedOverlayPausesWithoutRendering.

[Copilot]

Pull request overview

This PR fixes a hot-spin behavior when FrameRateLimit.Unlimited is used but rendering is effectively skipped (e.g., overlay hidden with pause policy, paused overlay, or target-paused). It does this by having the render callback report whether any frame work was actually performed, allowing the Win32 owner thread’s unlimited loop to briefly wait instead of continuously spinning.

Changes:

• Add a Windows integration test ensuring a hidden overlay with FrameRateLimit.Unlimited performs zero render callbacks/frames.
• Change OverlayWindow.RenderOneFrame to return bool indicating whether a render was actually performed.
• Extend the Win32 owner-thread frame-loop API to accept Func<bool> and use a short MsgWaitForMultipleObjectsEx wait in unlimited mode when no work was done.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
tests/ModernOverlay.Tests/OverlayWindowThreadingTests.cs	Adds a regression test for hidden + unlimited frame rate to ensure no rendering occurs.
src/ModernOverlay/OverlayWindow.cs	Makes per-frame render attempt report “did work” via a boolean return.
src/ModernOverlay.Win32/Win32OwnerThread.cs	Adds Func<bool> frame loop overload and introduces a brief wait when unlimited rendering is skipped.
src/ModernOverlay.Win32/Win32OverlayWindow.cs	Plumbs the new Func<bool> frame loop overload through the Win32 window wrapper.

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