KCL: Compute pipe expressions with loops, not recursion (#1941)

On `main`, the new test program in `tests/executor` causes a stack overflow. Running a flamegraph via `sudo cargo flamegraph --test executor -- serial_test_mike_stress_lines` shows that the problem: `fn execute_pipe_body` is very recursive. 

When there's a long pipe, `execute_pipe_body` executes the next child expression, which is always a CallExpression. So `execute_pipe_body` calls `CallExpression::execute`. Which then calls `execute_pipe_body` again. 

Fix is simple: `execute_pipe_body` now iterates over pipe subexpressions instead of recursing. This fixes the stack overflow, and is much faster too.

Closes https://github.com/KittyCAD/modeling-app/issues/1891.

src/wasm-lib/tests/executor/main.rs

@@ -142,6 +142,15 @@ const part002 = startSketchOn(part001, "start")
     twenty_twenty::assert_image("tests/executor/outputs/sketch_on_face_start.png", &result, 0.999);
 }
 
+#[tokio::test(flavor = "multi_thread")]
+async fn serial_test_mike_stress_lines() {
+    let code = include_str!("inputs/mike_stress_test.kcl");
+    let result = execute_and_snapshot(code, kittycad::types::UnitLength::Mm)
+        .await
+        .unwrap();
+    twenty_twenty::assert_image("tests/executor/outputs/mike_stress_test.png", &result, 0.999);
+}
+
 #[tokio::test(flavor = "multi_thread")]
 async fn serial_test_sketch_on_face_end() {
     let code = r#"fn cube = (pos, scale) => {
@@ -493,7 +502,7 @@ async fn serial_test_execute_i_shape() {
 }
 
 #[tokio::test(flavor = "multi_thread")]
-#[ignore] // ignore until more stack fixes
+#[ignore] // No longer a stack overflow problem, instead it causes an engine internal error.
 async fn serial_test_execute_pipes_on_pipes() {
     let code = include_str!("inputs/pipes_on_pipes.kcl");
 
@@ -514,7 +523,6 @@ async fn serial_test_execute_cylinder() {
 }
 
 #[tokio::test(flavor = "multi_thread")]
-#[ignore = "currently stack overflows"]
 async fn serial_test_execute_kittycad_svg() {
     let code = include_str!("inputs/kittycad_svg.kcl");