fix: handle psutil errors gracefully in _get_ncpus

[AlexanderFengler]

Summary

• Catches Exception around psutil.cpu_count to prevent SystemError on restricted environments (e.g. macOS sandbox, some CI runners)
• Implements an affinity-aware hierarchy (os.sched_getaffinity -> os.process_cpu_count -> os.cpu_count -> psutil) to prevent massive oversubscription on HPC clusters and SLURM allocations where the OS limits the cores available to the python process.
• If all cpu detection fails, raises a RuntimeError instead of silently falling back to 1 core, preventing unintended very slow simulations
• Adds a logger.info log message outputting the resolved number of cores so users can easily verify their config
• Adds a test verifying the new robust fallback behavior

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Flag	Coverage Δ
unittests	91.49% <100.00%> (+0.20%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
ssms/dataset_generators/lan_mlp.py	93.57% <100.00%> (+1.70%)	⬆️

... and 1 file with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.