Fix module test execution pattern with if __name__ == '__main__' guards

This change ensures tests run immediately when developing modules but don't execute when modules are imported by other modules.

Changes:
- Protected all test executions with if __name__ == "__main__" blocks
- Unit tests run immediately after function definitions during development
- Module integration test (test_module()) runs at end when executed directly
- Updated module-developer.md with new testing patterns and examples

Benefits:
- Students see immediate feedback when developing (python module_dev.py runs all tests)
- Clean imports: later modules can import earlier ones without triggering tests
- Maintains educational flow: tests visible right after implementations
- Compatible with nbgrader and notebook environments

Tested:
- Module 01 runs all tests when executed directly ✓
- Importing Tensor from tensor_dev doesn't run tests ✓
- Cross-module imports work without test interference ✓

modules/06_optimizers/optimizers_dev.py

@@ -345,6 +345,9 @@ def test_unit_optimizer_base():
 
     print("✅ Base Optimizer works correctly!")
 
+if __name__ == "__main__":
+    test_unit_optimizer_base()
+
 # %% [markdown]
 """
 ## SGD - Stochastic Gradient Descent
@@ -560,6 +563,9 @@ def test_unit_sgd_optimizer():
 
     print("✅ SGD optimizer works correctly!")
 
+if __name__ == "__main__":
+    test_unit_sgd_optimizer()
+
 # %% [markdown]
 """
 ## Adam - Adaptive Moment Estimation
@@ -803,6 +809,9 @@ def test_unit_adam_optimizer():
 
     print("✅ Adam optimizer works correctly!")
 
+if __name__ == "__main__":
+    test_unit_adam_optimizer()
+
 # %% [markdown]
 """
 ## AdamW - Adam with Decoupled Weight Decay
@@ -1039,6 +1048,9 @@ def test_unit_adamw_optimizer():
 
     print("✅ AdamW optimizer works correctly!")
 
+if __name__ == "__main__":
+    test_unit_adamw_optimizer()
+
 # %% [markdown]
 """
 ## 4. Integration: Bringing It Together
@@ -1409,7 +1421,8 @@ def test_module():
 
 # %%
 # Run comprehensive module test
-test_module()
+if __name__ == "__main__":
+    test_module()
 
 # %% [markdown]
 """