Report the spacing the writing line applies: the modelled line places
each run at the sum of the previous advances, so every space is 0.
Co-Authored-By: Claude Opus 5.5 <[email protected]>
Create, destroy, clear, write runs, step through them and read the
line metrics, following KytyPS5. Layouts from SharpProspero.
Co-Authored-By: Claude <[email protected]>