Add ancestor boxes to interface.

Implement finding box edges.

Allow extracting ResolvedBox from WithSpan.

Implement set operations on [ResolvedBox].

Allow extracting spacing from ResolvedBox.

Make paragraph direction explicit in tests.

Store direction in ResolvedBox.

Add required textDirection to TextOptions.

Link ResolvedSpan to boxes.

Use ResolvedBox when flattening trees.

Define ResolvedBox.

Improve code readability with type alias.

Separate WithSpan for sharing with other modules.

Test layout with mixed font sizes.

Deduplicate pagination code.

Test Rich pagination.

Implement Rich pagination.

Qualify Plain pagination.

Test Rich line wrapping.

Test Rich layout.