fix: Use float extension methods in Multiplayer sample

[tyevco]

Summary

The Multiplayer sample uses direct float comparison instead of the recommended FloatExtensions methods, violating CLAUDE.md guidelines and teaching anti-patterns.

Source: Code Review #682 (SAMPLE-1)

Location

samples/KeenEyes.Sample.Multiplayer/Components.cs:36-46

// CURRENT (lines 36-46):
public readonly uint GetDirtyMask(in Position baseline)
{
    uint mask = 0;
    if (MathF.Abs(X - baseline.X) > 0.001f)  // ❌ Direct float comparison
    {
        mask |= 1;
    }
    // ...
}

// SHOULD BE:
using KeenEyes.Common;

public readonly uint GetDirtyMask(in Position baseline)
{
    uint mask = 0;
    if (!X.ApproximatelyEquals(baseline.X))
    {
        mask |= 1;
    }
    // ...
}

Impact

• CLAUDE.md explicitly states "Never use == to compare floats"
• Sample code teaches anti-patterns that users will copy
• Inconsistent with other samples that use the extension methods

Priority

HIGH - Sample code quality affects all users learning from the codebase.