feat(rocke): make torch optional, not load-bearing

[shumway]

Motivation

rocKE is consumed downstream by PyTorch, so depending on torch is circular. torch was already absent from declared deps (pyproject pins only numpy) and the IR/emission path was torch-free, but it remained load-bearing at runtime and in the test suite: tests/run_all.py was RED (33 failed) without torch. This makes the torch-free suite GREEN.

Technical details

Runtime resolver (hip_module.py, comgr.py):

• The accidental dependency: rocKE relied on import torch to put ROCm's wheel-bundled libamd_comgr.so / libamdhip64.so on the loader path. A library must not import torch for a side effect. _candidate_lib_paths now discovers
  ROCm without torch: env override -> torch-bundled-if-already-imported ->
  $ROCM_PATH/$ROCM_HOME -> globbed /opt/rocm*/core-/lib & /opt/rocm/lib (newest first) -> bare soname. Eliminates 16 cannot load failures.
• Fix latent bug in resolved_lib_rocm_version(): on packaged ROCm 7.2 it read a component .info/version (7.13) instead of the ROCm release (7.2), which drives LLVM-flavor selection (llvm20 vs llvm22).

Tests (test_rocke.py):

• Gate the 17 genuinely torch-needing tests behind importorskip/skipUnless so they skip torch-free but still run in torch/GPU CI lanes (no coverage lost).
• Add a torch-free /dev/kfd GPU guard for 3 tests the resolver fix unmasked (they reached hipModuleLoadData and hung on a GPU-less box).
• Rewrite test_dtype_to_ir_accepts_torch_aliases to exercise the string path so it runs torch-free.

Docs (AGENTS.md, BUILD.md):

• Document torch as OPTIONAL (the three torch-only lanes vs the torch-free majority), the 5-tier ROCm library discovery order, the cannot load libamd_comgr.so -> set ROCM_PATH fix, and the new hard rule.

Test Plan

This is need prior to enabling automatic CI, so the test are just run local.

Setup a venv python from requirements.txt, which does not include torch. Verify that python tests/run_all.py runs correctly. It previously failed with import torch in several files.

Test Results

Verified torch-free: byte-identity gate GREEN (65/65), pytest 460 passed / 0 failed, relative-path guard PASS.

JIRA ID : AICK-1518

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