cultmath tests: the mirror twin count is 127 (span_rounding and span_slack twins)

EveryMirrorFunctionMatchesCSharpMath compared both new twins bit for bit against the C# seam;
only its pinned count of mirrored functions moves from 125 to 127. Builds.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

packages/cultmath/tests/CultMath.Tests/HlslSourceCompatibilityTests.cs

@@ -178,7 +178,7 @@ public sealed class HlslSourceCompatibilityTests
         }
 
         Assert.True(mismatches.Count == 0, $"{mismatches.Count} mismatches:{Environment.NewLine}{string.Join(Environment.NewLine, mismatches.Take(12))}");
-        Assert.Equal(125, compared.Count);
+        Assert.Equal(127, compared.Count);
     }
 
     /// <summary>