[codex] fix: clarify best-effort environment probe failures

[mldangelo-oai]

Summary

GitHub code scanning flagged several empty except OSError: pass blocks in src/promptfoo/environment.py.

Those handlers were intentional best-effort fallbacks around optional /proc and /sys probe files, so the findings are effectively false positives from a runtime behavior perspective. The downside was that the code made this intent implicit, which left the scanner and human readers with no explanation for why those exceptions were ignored.

Fix

This change centralizes optional probe-file reads in _read_probe_file(), which returns None when a probe file is missing or unreadable and documents why that fallback is safe for environment detection.

The Linux distro, cloud provider, container, and WSL detectors now call that helper instead of repeating inline try/except OSError blocks.

Validation

Ran:

• uv run ruff check src/ tests/test_environment.py
• uv run ruff format --check src/ tests/test_environment.py
• uv run mypy src/promptfoo/
• uv run pyright src/promptfoo/
• uv run pytest tests/test_environment.py