feat: convert regions into TableData

[maxmnemonic]

Added capability to load TableData.from_regions
Converts regions (lists of BoundingBox): rows, columns, merged cells into table_data structure,
Adds semantics for regions of row_headers, col_headers, row_section.
Tolerates slight overlaps "wobbly" bounding boxes, in some cases missing bounding boxes, etc.

Includes test_regions_to_table.py - that acts as an example

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[PeterStaar-IBM]

@maxmnemonic A few comments:

Direct Replacements

• bbox_fraction_inside(inner, outer, eps=...): replace with inner.intersection_over_self(outer).
• bbox_contains(inner, outer, threshold, eps=...): replace with inner.intersection_over_self(outer) >= threshold.
• bbox_iou(a, b, eps=...): replace with a.intersection_over_union(b, eps=eps).
• is_bbox_within(bbox_a, bbox_b, threshold=0.5): replace with bbox_b.intersection_over_self(bbox_a) >= threshold.
  • Note: this function’s parameter order is “is B within A”; keep call sites consistent.

Not Directly Replaceable

• bbox_intersection(a, b) -> Optional[BoundingBox]: no BoundingBox method returns the intersection box itself, only areas/ratios.
  This helper is still needed.
• dedupe_bboxes(...): no class method for deduplication; can be simplified internally by calling
  element.intersection_over_union(kept) directly, but not fully replaced.
• _process_table_headers(...), compute_cells(...), regions_to_table(...): table/semantics glue — not replaceable by a single
  BoundingBox method.

Notes

• All BoundingBox overlap/IoU methods assume matching coord_origin; same constraint applies today in regions.py.
• intersection_over_self already handles zero-area safely (returns 0). The small eps used in bbox_fraction_inside is unnecessary
  when switching.

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Codecov Report

❌ Patch coverage is 88.49558% with 13 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
docling_core/types/doc/document.py	92.70%	7 Missing ⚠️
docling_core/types/doc/base.py	64.70%	6 Missing ⚠️

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[vagenas]

Couple comments left inline.

[vagenas]

For reference: document.py modularization to be addressed in #433