Add Per-Corner Roundness to Rectangle Path: a checkbox (off by default) and four Pixels properties (top-left, top-right, bottom-right, bottom-left). New rectangles initialise the four values from their Roundness, so ticking the box keeps the shape; the radii are animatable and expression-driven.\n\nrect_radii() builds the path clockwise from the top-left with kappa quarter-circle arcs. Overlapping radii scale down like CSS border-radius; negative and non-finite radii are square; rect() delegates to it, so uniform roundness clamps to half the shorter side as before.\n\nLottie rc has one r: four equal static radii export as that value; mixed or animated radii export roundness 0 with a warning. Import puts r into the four per-corner values so ticking the box on an imported rectangle keeps the shape.\n\nTests: path geometry and clamping, rendered per-corner pixels, Lottie equal/mixed/checkbox-off export.
render: upstream moved the tests_*.rs modules into crates/render/src/tests/; the branch's
tests_mask_feather.rs now lives at tests/mask_feather.rs and is registered in tests.rs.
path: rect() keeps the branch's explicit-outline version with an added NaN guard on the
roundness clamp bound (main's fix for the same panic).
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Camille Moine