Consolidate tree types into one.

Handle ancestor boxes in rich layout.

Add ancestor boxes to interface.

Implement finding box edges.

Allow extracting ResolvedBox from WithSpan.

Implement set operations on [ResolvedBox].

Allow extracting spacing from ResolvedBox.

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.

Deduplicate pagination code.

Implement Rich pagination.

Qualify Plain pagination.

Make paginateAll generic.

Implement piecewise paragraph construction.

Refactor pagination to allow rich layout.