Indent code in speaker notes (#476)

* Indent code in speaker notes

#475

* Update stack.md

* Update destructuring-arrays.md

* Update hashmap.md

* Update traits.md

src/memory-management/stack.md

@@ -31,20 +31,20 @@ fn main() {
 
 * We can inspect the memory layout with `unsafe` code. However, you should point out that this is rightfully unsafe!
 
-```rust,editable
-fn main() {
-    let mut s1 = String::from("Hello");
-    s1.push(' ');
-    s1.push_str("world");
-    // DON'T DO THIS AT HOME! For educational purposes only.
-    // String provides no guarantees about its layout, so this could lead to
-    // undefined behavior.
-    unsafe {
-        let (capacity, ptr, len): (usize, usize, usize) = std::mem::transmute(s1);
-        println!("ptr = {ptr:#x}, len = {len}, capacity = {capacity}");
+    ```rust,editable
+    fn main() {
+        let mut s1 = String::from("Hello");
+        s1.push(' ');
+        s1.push_str("world");
+        // DON'T DO THIS AT HOME! For educational purposes only.
+        // String provides no guarantees about its layout, so this could lead to
+        // undefined behavior.
+        unsafe {
+            let (capacity, ptr, len): (usize, usize, usize) = std::mem::transmute(s1);
+            println!("ptr = {ptr:#x}, len = {len}, capacity = {capacity}");
+        }
     }
-}
-```
+    ```
 
 </details>