Fix direct NVML compatibility and optional metadata handling

[Qubitium]

Summary

• route absent direct NVML symbols through controlled errors and select PCI info v3, v2, then legacy with ABI-correct ctypes layouts
• restrict PCI compatibility fallback to NVML NOT_SUPPORTED/FUNCTION_NOT_FOUND responses
• route GPU and MIG identifiers correctly, normalize CUDA visibility entries, and reject malformed interior empty entries
• preserve usable NVML device data when optional VBIOS, compute-capability, or PCIe metadata is unavailable
• make NVML shutdown safe and idempotent

Verification

• focused NVML tests: 32 passed
• full suite: 52 collected, 48 passed, 4 skipped
• Ruff checks: passed
• isort --check-only: passed
• git diff --check: passed
• sdist build: passed
• twine check: passed

Environment limitations

The four full-suite skips are GPU integration tests because this runner has no detectable GPU and lacks lspci. The direct NVML behavior is covered with ctypes-based regression tests.

Deferred findings

No unrelated cleanup or additional findings were included; scope is limited to the confirmed direct NVML defects.