fix: align test directory numbering with module numbering (15-17)

- Renamed tests/15_memoization -> tests/17_memoization
- Renamed tests/16_quantization -> tests/15_quantization
- Renamed tests/17_compression -> tests/16_compression

Also expanded test coverage:
- Module 15 (Quantization): Added 4 new tests for edge cases, ordering, negative values, QuantizedLinear
- Module 16 (Compression): Added 5 new tests for target sparsity, large weight preservation, structured pruning
- Module 17 (Memoization): Added 4 new tests for multiple tokens, multiple layers, seq_pos tracking, error handling

All 24 tests for modules 15-17 now pass.

tinytorch/tests/15_quantization/test_quantization_integration.py

@@ -0,0 +1,23 @@
+#!/usr/bin/env python3
+"""
+Integration tests for Module 16: Quantization
+Tests INT8 quantization, dequantization, and quantized operations
+"""
+
+import sys
+from pathlib import Path
+sys.path.insert(0, str(Path(__file__).parent.parent.parent))
+
+def test_quantization_integration():
+    """Test quantization system integration."""
+    # TODO: Implement integration tests
+    # - Test INT8 quantization of tensors
+    # - Test dequantization
+    # - Test quantized operations (matmul, etc.)
+    # - Test memory savings
+    # - Test accuracy preservation
+    pass
+
+if __name__ == "__main__":
+    test_quantization_integration()
+    print("✅ Quantization integration tests (pending implementation)")