[infra] Enable CPU-only development: bindings stubs, profiler fix, conftest guard

[tburt-nv]

Description

Makes the tensorrt_llm wheel importable on machines without an NVIDIA GPU driver, while preferring the real compiled C++ bindings when available.

Design

The bindings/ directory is now a Python package instead of a single compiled .so module. On import it follows a two-tier strategy:

bindings/__init__.py
  ├── try:  from ._C import *          ← real pybind11 .so (GPU machine)
  └── except ImportError:              ← Python-only stubs  (CPU machine)
          __getattr__ = make_module_getattr(...)

Environment	What happens
GPU machine with compiled wheel	Real _C.so loads → full bindings
CPU machine with compiled wheel	_C.so fails (no libcuda.so) → stubs activate, _init() logs warning
CPU machine without wheel libs	No _C.so present → stubs activate

Changes

tensorrt_llm/bindings/__init__.py — try real _C extension, fall back to stubs. No TRT_LLM_NO_LIB_INIT env var needed.

tensorrt_llm/_common.py — _init() catches OSError from missing native .so libs and logs a warning instead of crashing.

scripts/build_wheel.py — compiled pybind .so is placed as bindings/_C.cpython-*.so (inside the package) so it coexists with the stub fallback.

setup.py — updated package_data glob; extract_from_precompiled handles both new (bindings/_C.*) and legacy (bindings.*) wheel layouts by relocating legacy files automatically.

tensorrt_llm/bindings/_stubs.py — DRY shared metaclass (unchanged from previous commit).

tensorrt_llm/profiler.py — graceful pynvml.NVMLError handling (unchanged from previous commit).

tests/unittest/conftest.py — torch.cuda.is_available() guard (unchanged from previous commit).

Test Coverage

35 CPU-compatible unit tests pass — no environment variables required:

python3 -m pytest \
  tests/unittest/llmapi/test_reasoning_parser.py \
  tests/unittest/llmapi/test_build_cache.py \
  tests/unittest/others/test_mapping.py \
  tests/unittest/trt/quantization/test_mode.py \
  tests/unittest/others/test_kv_cache_manager.py \
  tests/unittest/others/test_module.py -v

unit_tests_final.log

All 21 pre-commit hooks pass.

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