[Test][ROCm] Account for gfx950 FP8 RMSNorm rounding

[AndreasKaratzas]

Summary

• Use the shared FP8 allclose contract only for the measured gfx950 fused RMSNorm cases.
• Bound every accepted difference to one FP8 ULP while leaving scales, residuals, other dtypes, other architectures, and other ROCm checks unchanged.

E4M3 adjacent codes can differ by 12.5%, and its minimum subnormal step is approximately 0.002. Fused and unfused gfx950 reductions selected adjacent codes at those boundaries; no production kernel changed.

Validation

• Original Buildkite failures: 39 passed.
• Final changed scope: 162 static cases passed; dynamic scope had 304 passed and 152 expected parameter skips.
• Earlier complete matrices passed 648 static and 1,128 dynamic cases; changed-file pre-commit passed.

Buildkite: Kernels Core Operation

Duplicate check: no open PR covers these tests; #49621 changes separate per-group quantization files.

AI assistance: Codex assisted with investigation, implementation, and validation; Andreas directed the numerical contract and reviewed the resulting changes.