Python(feat): hierarchical pytest report tree (packages, modules, classes, parametrize)

[alexluck-sift]

Summary

• Hierarchical report tree: Python packages, test modules, test classes (including nested), and @pytest.mark.parametrize axes now each open a nested parent step automatically via a unified diff-stack mechanism. The old module_substep fixture is removed; everything above the leaf is handled by one autouse _hierarchy_parents fixture.
• Identity-aware diff keyed by node.nodeid (not just name), so two same-named ancestors reached via different paths (e.g. proj_a/utils and proj_b/utils in a monorepo) stay distinct in the report tree.
• Four ini opt-outs gate the new layers individually: sift_package_step, sift_module_step, sift_class_step, sift_parametrize_nesting (all default true). Frames stay in the diff for identity even when their layer is gated off.
• New step.measurements_passed property on NewStep for the assert step.measurements_passed end-of-test pattern: fails pytest when any bounds check on this step failed, without short-circuiting on individual measure(...) calls.
• Drain ordering fix: hierarchy parents now drain inside ReportContext.__exit__ (was draining in pytest_sessionfinish after the import worker had already shut down, leaving parents stuck IN_PROGRESS in Sift).
• Import worker timeout bumped 1s → 30s; replay instructions now point at the correct import-test-result-log binary; replay failures emit SiftPytestStepDrainWarning instead of a silent logger.error.
• Defensive drain: per-frame __exit__ failures during teardown warn and continue; mid-session drains use a strict variant that re-raises so genuine invariant violations surface as test errors.
• Runnable demo at python/examples/pytest_plugin/ plus a new pytest_plugin_quickstart.md mkdocs page that snippets the demo files. pytest_plugin.md updated for the new ini knobs.
• Tests: test_hierarchy.py pytester suite covers classes, nested classes, packages, opt-out flags, cross-path collisions, and the drain helper; integration test covers the new step.measurements_passed property.

[github-actions]

Python docs preview: https://sift-stack.github.io/sift/python/pr-570/

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