Sketch profiles: grid-accelerated splitting and node merging, bounding-box nesting (large sketches several times faster); randomized sketch-editing test (thousands of mixed create/modify/constraint/projection/undo steps: no panics, designs round-trip)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AS5Tn3xieewUSg3uxrMVdL

crates/engine/src/cmd/sketch_constraints.rs

@@ -514,3 +514,7 @@ fn snap(s: &mut Session, p: &Value) -> Result<Value> {
 #[cfg(test)]
 #[path = "sketch_constraints_tests.rs"]
 mod tests;
+
+#[cfg(test)]
+#[path = "sketch_fuzz_tests.rs"]
+mod fuzz;