Wire PE-US-data L0 calibration backend

[MaxGhenis]

Summary

• add a lazy PE-US-data fit_l0_weights wrapper for Microplex's pe_l0 adapter
• wire calibration_backend=pe_l0 to pass the incumbent L0 optimizer hook from the pipeline factory
• cover wrapper argument filtering and factory hook regressions

Validation

• uv run --python 3.13 --extra dev ruff check src/microplex_us/pipelines/pe_l0.py src/microplex_us/pipelines/us.py tests/pipelines/test_pe_l0.py tests/calibration/test_us_pipeline_dispatch.py
• uv run --python 3.13 --extra dev ruff format --check src/microplex_us/pipelines/pe_l0.py src/microplex_us/pipelines/us.py tests/pipelines/test_pe_l0.py tests/calibration/test_us_pipeline_dispatch.py
• uv run --python 3.13 --extra dev python -m pytest tests/pipelines/test_pe_l0.py tests/calibration/test_us_pipeline_dispatch.py::test_pe_l0_deferred_stage_disables_sparsity_penalty