Add non-gating artifact transparency sidecars

[MaxGhenis]

Summary

• add microplex-us-write-transparency-sidecars for source, imputation, column, row-count, and calibration JSON sidecars
• mark generated sidecars as non-gating with production_performance_gate: loss
• parse long-build logs so active artifacts can expose donor progress before the H5 exists

Validation

• uv run --extra dev ruff check src/microplex_us/pipelines/transparency_sidecars.py tests/pipelines/test_transparency_sidecars.py pyproject.toml
• uv run --extra dev ruff format --check src/microplex_us/pipelines/transparency_sidecars.py tests/pipelines/test_transparency_sidecars.py
• uv run --extra dev pytest tests/pipelines/test_transparency_sidecars.py

Notes

This is observability only; it does not add a production gate beyond the loss comparison.