Musa support native kernels

[Arlo-mt]

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[zhangj1an]

Thanks! It is already almost there, after addressing the following we can merge it.

Please refer to PR 204 (#204) as an example when adding new kernels.

1. Test breakage: tests/test_rms_norm.py calls torch.musa.is_available() unguarded and fails with AttributeError on non-MUSA platforms (verified). Use device_ctx.is_musa or a hasattr guard.
2. Please register musa kernels in rl_engine/kernels/gtest/operator_specs.py ("musa" candidates), docs/operators/*.md Backends rows, rl_engine/_C.pyi stubs for the new symbols, and a benchmark script.
3. Bitwise evidence: for copy/elementwise ops (embedding/rope/silu/swiglu) add torch.equal bitwise tests vs the same-dtype PyTorch reference (fp32 internally, single cast at the end); for reductions (logp/lm_head/rmsnorm/attention/det_gemm) add bitwise batch-invariance tests + contract-tolerance accuracy tests, mirroring tests/test_batch_invariant_logp.py.
4. Please rebase your branch on the test branch and change the PR base to test. Also update TestMusaPlatform expectations (the native-first musa map conflicts with the current assertions on both main and test), and coordinate the musa priority map with #375 (decide merge order / final native-first + triton-fallback map).
5. Fix DCO sign-off and the unreachable device_ctx.is_musa branch in tests/test_logp.py.