fix(tests): repair solid_model tri_count helper after upstream merge

mesh_from_solid was removed in the upstream merge; use tessellation(body).mesh.triangles directly.

src/scene/model/solid_model.rs

@@ -441,9 +441,7 @@ mod tests {
     use super::*;
 
     fn tri_count(body: &Body) -> usize {
-        mesh_from_solid(body, [0.7, 0.7, 0.7, 1.0])
+        tessellation(body).mesh.triangles.len()
-            .map(|m| m.lods[0].indices.len() / 3)
-            .unwrap_or(0)
     }
 
     #[test]