Add PyTorch support to TPU Raiden H2D/D2H presubmit performance gating.

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Add PyTorch support to TPU Raiden H2D/D2H presubmit performance gating.

Implement automated presubmit performance regression gating for the PyTorch path in TPU Raiden (third_party/tpu_raiden/tpu_sync/benchmarks/), establishing parity with JAX.

Key changes:

• Decouple perf_core.py under a unified, narrow public function measure(...) that supports both framework="jax" and framework="torch". Callers do not need to know about framework-specific runtime setups, memory pinning, or worker multi-processing.
• Add PyTorch SPMD multi-processing transfer execution (_torch_worker_fn) using torch.multiprocessing.spawn, rank synchronization via dist.all_reduce (MIN/MAX wall-clock timing across ranks), and pre-measurement byte-integrity verification.
• Update h2d_d2h_benchmark_gating.py to default to --framework=all (with selective --framework=jax|torch support), gating both frameworks in a single unified run on physical TPU hardware.
• Unify test shapes and baselines in h2d_d2h_gating_baselines.json under a single hardware configs list, holding both JAX and PyTorch to the same physical DMA throughput floors without artificial branching.
• Update h2d_d2h_gating in benchmark_registry.pbtxt and h2d_d2h_record in benchmark_registry_record.pbtxt with symmetrical JAX (jax_...) and PyTorch (torch_...) metrics, plus legacy un-prefixed aliases to maintain continuous tracking on go/tpu-sync-oss-mlcompass.
• Register h2d_d2h_benchmark_gating_torch_gl and h2d_d2h_benchmark_gating_gl test targets and add PyTorch dependencies to BUILD.
• Update H2D_D2H_GATING_TEST.md documentation.

Tested:

• blaze-for-agents build -c opt //third_party/tpu_raiden/tpu_sync/benchmarks:all passed.
• Formatted via hg fix.

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