- Record original and reduced font sizes, line spacings and paragraph
spacings as multisets, so restoring neighbouring sizes clears the
exhausted budget, and paragraph spacing keeps the budget when line
spacing rounds back to its original.
- Resolve font and spacing budgets independently, letting the remaining
component be used instead of refusing the whole command.
- Persist FitState in a namespaced DOCX custom XML part and restore it on
read; add a DOCX round-trip regression.