docs: document MaxTime's WarningTime warning threshold (NUnit 5)

[Copilot]

NUnit 5 added a WarningTime named parameter to MaxTimeAttribute (nunit/nunit#5261) — if a test exceeds the warning threshold but still completes within the failure limit, the result is Warning rather than Failure. This was not documented.

Changes

• maxtime.md — Added a "Named Parameters" table for WarningTime, a "Warning Threshold" example section, and a note clarifying the soft-threshold semantics.
• MaxTimeAttributeExamples.cs — Added #region MaxTimeWarningThreshold snippet referenced by the docs.

[Test]
[MaxTime(1000, WarningTime = 200)]
public void OperationWithWarningThreshold()
{
    // Completes within 1000ms → Pass
    // Exceeds 200ms but under 1000ms → Warning
    // Exceeds 1000ms → Failure
    PerformOperation();
}

[stevenaw]

@copilot The build failure is because the snippets project is not using the latest alpha package. Please update the project to use NUnit version 5.0.0-alpha.100.9

[Copilot]

@copilot The build failure is because the snippets project is not using the latest alpha package. Please update the project to use NUnit version 5.0.0-alpha.100.9

Updated the NUnit package reference to 5.0.0-alpha.100.9 in Snippets.NUnit.csproj — build passes locally with the new version.

[OsirisTerje]

Nice!