Render: a moved path reuses its stroke outline

A path object that moves without changing shape drew its stroke by
outlining the whole line again, because the stroke outline cache is
keyed by the node. The renderer now keeps, per object, stroke and
outline width, the latest outline with the line it was made from. When
the new line is that line moved, it draws the kept outline moved by the
same offset, and moves the region a long path was outlined in with it.

Scaling, rotating or editing the path, changing the stroke's width,
join, cap, dashes or profile, a zoom that changes the outline's
tolerance, and a move that takes the view past the outlined region
still outline the stroke again. Only the latest outline of each stroke
keeps its line.

docs/target-app-parity.md

@@ -1268,6 +1268,7 @@ Moved from the ROADMAP's "Shipped so far" on 2026-10-10. Update it when a featur
   With more than 10,000 type on a path objects selected, the Selection and Direct Selection tools neither draw nor hit-test the objects' brackets.
   The renderer outlines the stroke of a path object with more than 1,024 path elements, without dashes or a width profile, only in and around the view, with a margin of the view's size on each side, and outlines it again when the view moves past that margin. The pixels are the same. At 1600 × 1200, the frame after one anchor of an open path of 200,000 anchors moves takes 28 to 30 ms instead of 103 ms, and with a closed path of 50,000 anchors 10 ms instead of 30 ms (`cargo run --release -p vectorcraft-engine --example anchor_bench`).
   The renderer outlines a dashed stroke of such a path the same way, without a width profile, and draws its dashes and dots in the same places as when the whole path is dashed, so the pixels are the same. A pattern too fine to draw is drawn solid, as before, and its stroke is outlined near the view too. At 1600 × 1200, the frame after one anchor moves takes 14 ms instead of 102 ms with a filled closed path of 50,000 anchors and a stroke of 6 pt dashes and 4 pt gaps (`cargo run --release -p vectorcraft-engine --example anchor_bench`, which now includes that document).
+  When a path object moves without changing shape, the renderer draws its stroke from the outline it made before the move, moved by the same offset. It outlines the stroke again when the path is scaled, rotated or edited, when the stroke changes, and when the move takes the view past the part of a long path it outlined. The pixels are the same. At 1600 × 1200, the frame after a 1 pt nudge takes 128 ms instead of 405 ms with an open path of 200,000 anchors in view (104 ms with nothing changed), and 14 ms instead of 28 ms with a closed path of 50,000 anchors whose stroke is dashed and has a width profile.
   The renderer keeps the path of a path or compound path of 1,024 anchors or more by object, with the bounds of its segments and of its miter spikes in runs of 128 segments. When anchors move and the subpaths and anchor counts stay the same, the next frame changes only the segments that start or end at a moved anchor and measures again only the runs that hold them or the segments with length before them, instead of making the whole path again and measuring it whole for culling. The pixels and the cull bounds are the same. On Windows at 1600 × 1200, the frame after one anchor moves takes 8.2 ms instead of 30.1 ms with an open path of 200,000 anchors, 4.3 ms instead of 10.4 ms with a closed path of 50,000 anchors, and 6.6 ms instead of 11.9 ms with the filled closed path of 50,000 anchors and a dashed stroke (medians of five runs of `anchor_bench`).
   Type › Show Hidden Characters keeps the marks it places on each text object from one frame to the next. The canvas lays a text object out again when an edit changes it or its threaded story, or when the last frame that showed the marks did not draw it, and it lays out all type in view again when the fonts or the hyphenation exceptions change. With 1,000 two-line labels in view, drawing the marks takes 0.8 ms per frame in a release build instead of 19.7 ms.
   A selection with more than 100,000 points to outline shows its bounds instead of each object's outline and anchors. Paths count their anchors. Area type and type on a path count the anchors of their frame or path, and point type counts six: its box's corners and the ends of its baseline marker. Images, symbol instances, placed documents, and area type or type on a path in perspective count the four corners of their box, and gradient meshes and envelopes count their points and the ends of their mesh lines. The hover highlight leaves out an object past that count, and such an object shows its bounds as the key object. With 32,768 type objects, images, symbol instances, gradient meshes or envelopes selected, the selection's outlines and anchors add fewer than 100 vertices to the canvas's mesh (#2460).