fix: apply filtered read limit after refine filter

[Xuanwo]

FilteredReadExec could spend a pushed-down LIMIT on scalar-index matches before evaluating a remaining refine filter, which allowed filtered scans to return fewer rows than requested even when enough rows matched the full predicate.

This keeps scalar-index range truncation behind the full-filter exactness boundary: indexed candidates are still narrowed by the scalar index, but scan_range_after_filter is only consumed early when no refine filter remains. Regression coverage exercises both the FilteredReadExec path and the scanner(filter, limit) end-to-end behavior.

Fixes lancedb/lancedb#3436.

[claude]

Claude Code Review

This repository is configured for manual code reviews. Comment @claude review to trigger a review and subscribe this PR to future pushes, or @claude review once for a one-time review.

_{Tip: disable this comment in your organization's Code Review settings.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[Xuanwo]

@claude review once

[claude]

⚠️ Code review skipped — your organization has reached its monthly code review spending cap.

An organization admin can view or raise the cap at claude.ai/admin-settings/claude-code. The cap resets at the start of the next billing period.

Once the cap resets or is raised, comment @claude review on this pull request to trigger a review.