A generated many-part assembly: test and open-phase benchmark (#927)

Generates N parts of four primitive bodies, each moved into a placed component. The test (12 parts) checks the open, the world placement and the saved round trip; the ignored bench_generated_assembly prints parse, evaluation inside and outside the features, mesh warm-up and Measure.

crates/engine/src/lib.rs

@@ -812,6 +812,8 @@ mod extent_tests;
 #[cfg(test)]
 mod hole_face_tests;
 #[cfg(test)]
+mod large_assembly_tests;
+#[cfg(test)]
 mod naming_history_tests;
 #[cfg(test)]
 mod pattern_suppress_tests;