* ⚡ Keep only the shape data the worker reads
The worker kept a full copy of the current page for its selection and
snap indexes. It now keeps only the attributes the indexes and the
change replay read, and re-indexes only the shapes that changed.
On a 52k-shape page the worker heap goes from 698 MB to 286 MB.
Closes#12740
AI-assisted-by: claude-opus-5-5
* ♻️ Share the worker re-trim with its replay test
The worker and its replay test now share `retrim-objects`.
AI-assisted-by: claude-opus-5-5