fix: Correctly evaluate pl.len() with lazy validation in plan

[Oliver Borchert (borchero)]

Motivation

Moritz Potthoff (@MoritzPotthoffQC) discovered a bug where pl.len() was reported incorrectly.

[Copilot]

Pull request overview

This PR fixes an incorrect pl.len() result when using pl.scan_parquet(...).pipe(schema.validate, eager=False) by adjusting the Polars plugin fast-path for the “no rule failures” case, and adds coverage to prevent regressions.

Changes:

• Add a regression test asserting pl.len() remains correct after lazy validation on a scanned parquet.
• Update the Rust all_rules_required plugin to return an all-true boolean bitmap (length = input) when there are no validation failures, to support a filter fast-path.
• Extend the row-wise validation benchmark to parameterize eager vs lazy validation.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
tests/schema/test_validate.py	Adds a regression test for lazy validation over scan_parquet ensuring pl.len() stays correct.
tests/benches/test_schema.py	Updates benchmark to cover both eager and lazy validation modes.
src/polars_plugin/mod.rs	Changes all_rules_required success-path output to a full-length all-true bitmap series to avoid incorrect lazy plan behavior.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (0cbc66a) to head (83cae0a).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #371   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files           56        56           
  Lines         3507      3507           
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  Hits          3507      3507           

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