Fix module dependency chain - clean imports now work

Critical fixes to resolve module import issues:

1. Module 01 (tensor_dev.py):
   - Wrapped all test calls in if __name__ == '__main__': guards
   - Tests no longer execute during import
   - Clean imports now work: from tensor_dev import Tensor

2. Module 08 (dataloader_dev.py):
   - REMOVED redefined Tensor class (was breaking dependency chain)
   - Now imports real Tensor from Module 01
   - DataLoader uses actual Tensor with full gradient support

Impact:
- Modules properly build on previous work (no isolated implementations)
- Clean dependency chain: each module imports from previous modules
- No test execution during imports = fast, clean module loading

This resolves the root cause where DataLoader had to redefine Tensor
because importing tensor_dev.py would execute all test code.

modules/08_dataloader/dataloader_dev.py

@@ -70,23 +70,11 @@ import os
 import gzip
 import urllib.request
 import pickle
+import sys
 
-# Simplified Tensor class for DataLoader module
-# This avoids importing the full tensor_dev.py which executes all tests
-class Tensor:
-    """
-    Simplified Tensor class for DataLoader module.
-    Contains only the functionality needed for data loading.
-    """
-    def __init__(self, data):
-        self.data = np.array(data)
-        self.shape = self.data.shape
-
-    def __len__(self):
-        return len(self.data)
-
-    def __repr__(self):
-        return f"Tensor({self.data})"
+# Import real Tensor class from Module 01
+sys.path.append(os.path.join(os.path.dirname(__file__), '..', '01_tensor'))
+from tensor_dev import Tensor
 
 # %% [markdown]
 """
@@ -221,7 +209,7 @@ def test_unit_dataset():
 
     print("✅ Dataset interface works correctly!")
 
-test_unit_dataset()
+# test_unit_dataset()  # Moved to main block
 
 
 # %% [markdown]
@@ -400,7 +388,7 @@ def test_unit_tensordataset():
 
     print("✅ TensorDataset works correctly!")
 
-test_unit_tensordataset()
+# test_unit_tensordataset()  # Moved to main block
 
 
 # %% [markdown]
@@ -627,7 +615,7 @@ def test_unit_dataloader():
 
     print("✅ DataLoader works correctly!")
 
-test_unit_dataloader()
+# test_unit_dataloader()  # Moved to main block
 
 
 # %% [markdown]
@@ -840,7 +828,7 @@ def test_unit_download_functions():
 
     print("✅ Download functions work correctly!")
 
-test_unit_download_functions()
+# test_unit_download_functions()  # Moved to main block
 
 
 # %% [markdown]
@@ -991,7 +979,7 @@ def analyze_dataloader_performance():
     print("• Memory usage scales linearly with batch size")
     print("🚀 Production tip: Balance batch size with GPU memory limits")
 
-analyze_dataloader_performance()
+# analyze_dataloader_performance()  # Moved to main block
 
 
 def analyze_memory_usage():
@@ -1035,7 +1023,7 @@ def analyze_memory_usage():
     print(f"  Large batch (512×784): {large_bytes / 1024:.1f} KB")
     print(f"  Ratio: {large_bytes / small_bytes:.1f}×")
 
-analyze_memory_usage()
+# analyze_memory_usage()  # Moved to main block
 
 
 # %% [markdown]
@@ -1116,7 +1104,7 @@ def test_training_integration():
 
     print("✅ Training integration works correctly!")
 
-test_training_integration()
+# test_training_integration()  # Moved to main block
 
 
 # %% [markdown]
@@ -1176,13 +1164,29 @@ def test_module():
     print("Run: tito module complete 08")
 
 # Call before module summary
-test_module()
+# test_module()  # Moved to main block
 
 
 # %%
 if __name__ == "__main__":
     print("🚀 Running DataLoader module...")
+
+    # Run all unit tests
+    test_unit_dataset()
+    test_unit_tensordataset()
+    test_unit_dataloader()
+    test_unit_download_functions()
+
+    # Run performance analysis
+    analyze_dataloader_performance()
+    analyze_memory_usage()
+
+    # Run integration test
+    test_training_integration()
+
+    # Run final module test
     test_module()
+
     print("✅ Module validation complete!")