Standardize section headers for 04_layers module

modules/source/04_layers/layers_dev.py

@@ -252,6 +252,11 @@ def matmul(A: np.ndarray, B: np.ndarray) -> np.ndarray:
     return C
     ### END SOLUTION
 
+# %% [markdown]
+"""
+## 🔧 DEVELOPMENT
+"""
+
 # %% [markdown]
 """
 ### 🧪 Test Your Matrix Multiplication