feat: vendor MXFP8 MoE runtime

[S1ro1]

Summary

• Add a Python-only mxfp8_moe kernel package with differentiable grouped GEMM and explicit MXFP8 expert-parallel transport.
• Keep BF16 parameters and tensors at the public boundary; quantized data and scales remain internal.
• Vendor the orchestration from torchao commit 02105d46c with its BSD license and wide-MoE/large-tensor handling.
• Extend the kernel manifest, registry, and wheel builder to support Python-only kernels and runtime requirements.

Validation

• Built a wheel with PRIME_KERNELS=mxfp8_moe and PRIME_KERNELS_REQUIRE=1 and verified the module, manifest, and license are included.
• Imported the public module against the pinned torchao build.
• Ruff check, Ruff format check, and diff checks pass.
• The registry rejects the kernel on H200 before import as expected. Numerical execution still requires an SM100 runner.