feat: update workspace paths and enhance gitignore

- Updated stablediffusion crate path from "../stable-diffusion-burn" to "./crates/stable-diffusion-burn" for proper workspace resolution
- Enhanced .gitignore to include generated model files (.mpk, .pt, .bin, .safetensors, .ckpt) and user_data directory
- Added Cargo.lock to gitignore with appropriate comment
- Reorganized IDE files section in gitignore for better clarity
- Added newline at end of file for proper formatting

crates/stable-diffusion-burn/burn-crates/burn-backend-tests/tests/autodiff/expand.rs

@@ -0,0 +1,39 @@
+use super::*;
+use burn_tensor::TensorData;
+
+#[test]
+fn should_diff_expand() {
+    // Python code to generate the test case values
+    // import torch
+    // x1 = torch.tensor([4.0, 7.0, 2.0, 3.0], requires_grad=True)
+    // x2 = torch.tensor([2.0, 4.5, 7.0, 3.0], requires_grad=True)
+    // y = x1.expand(4, 4)
+    // z = (x2 * y).sum()
+    // z.backward()
+    // print("x1", x1.grad)
+    // print("x2", x2.grad)
+
+    let device = Default::default();
+
+    let data_1 = TensorData::from([4.0, 7.0, 2.0, 3.0]);
+    let tensor_1 = TestAutodiffTensor::<1>::from_data(data_1, &device).require_grad();
+
+    let data_2 = TensorData::from([2.0, 4.5, 7.0, 3.0]);
+    let tensor_2 = TestAutodiffTensor::<1>::from_data(data_2, &device).require_grad();
+
+    let tensor_3 = tensor_1.clone().expand([4, 4]);
+
+    // Use unsqueeze to make tensor_2 have the same shape as tensor_3
+    let tensor_4 = tensor_2.clone().unsqueeze().mul(tensor_3).sum();
+    let grads = tensor_4.backward();
+
+    let grad_1 = tensor_1.grad(&grads).unwrap();
+    let grad_2 = tensor_2.grad(&grads).unwrap();
+
+    grad_1
+        .to_data()
+        .assert_eq(&TensorData::from([8., 18., 28., 12.]), false);
+    grad_2
+        .to_data()
+        .assert_eq(&TensorData::from([16., 28., 8., 12.]), false);
+}