chore: add boolean match plan scaffold

[BubbleCal]

This is part 1 of improving boolean query performance

Summary

• Introduce an internal BooleanMatchPlan that normalizes match-only boolean FTS queries into a single-column plan.
  Add unit tests covering valid/invalid plan construction.
• No runtime behavior changes yet; this is a prep step for WAND-based boolean execution.
  Motivation
• Current boolean FTS planning drops limit, preventing WAND pruning. This PR lays the groundwork for an index-level boolean execution path by providing a normalized, index-executable plan.

[github-actions]

Code Review

This scaffold for BooleanMatchPlan looks solid overall. The code is well-structured with good test coverage for the various rejection cases.

Minor suggestions (not blocking):

1. Consider using std::borrow::Cow for the column field if performance becomes a concern - currently cloning the column string on every push_match call. However, this is likely negligible for typical query sizes.

2. Duplicate logic in try_build - The three loops for should/must/must_not have identical structure. Consider extracting to a helper to reduce repetition.

No P0/P1 issues identified. Good test coverage for edge cases (mixed columns, non-match queries, only must_not, missing column).

[codecov]

Codecov Report

❌ Patch coverage is 95.83333% with 4 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
rust/lance-index/src/scalar/inverted/query.rs	95.83%	1 Missing and 3 partials ⚠️

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