#9 Add noise-floor calibration

[iray-tno]

Summary

• add prepkit test suite noise-floor FILE cases for same-solver calibration
• run self-paired evaluations to estimate inherent numeric score variance
• report per-pair absolute deltas, mean absolute diff, max absolute diff, and signed diff stdev

Tests

• uv run pytest tests/test_test_command.py -q
• uv run pytest -q