* fix: improve heuristic table detection for numeric columns and multi-line headers
Two fixes for tables that have clean extractable text but fail heuristic
structure detection:
1. Numeric column merge pass (grid.rs): After initial X-position
clustering, adjacent clusters are merged when one is sparse (header
text) and the other is dense with >50% numeric items (data column).
Multi-line wrapped headers often land slightly offset from their
data column — the merge closes gaps within 1.5× the clustering
threshold. New is_numeric_text() helper matches decimals, percentages,
negative numbers, and comma-separated thousands.
2. Duplicate-header skip (detect_heuristic.rs): Spanning super-headers
like "First Degree | First Degree | Higher Degree" contain duplicate
cells that trigger looks_like_partial_table_ex rejection. Now skips
rows with duplicate cells when a better header candidate exists
within the next 3 rows (higher fill ratio or numeric cells).
Tested on BITS Pilani university report (430 pages, 314 table pages).
Page 4 (multi-line header + numeric data) previously returned
needs_ocr=true; now correctly detects the table structure.
Eval: 197 PDFs, zero regressions, all 104+ tests pass, zero clippy.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
* bump version to 0.7.1
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Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
