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/sign.rs

@@ -0,0 +1,42 @@
+use super::*;
+use burn_tensor::TensorData;
+
+/// Example using the sign function with PyTorch:
+// >>> import torch
+// >>> # Create a tensor with requires_grad=True
+// >>> x = torch.tensor([-2.0, -1.0, 0.0, 1.0, 2.0], requires_grad=True)
+// >>> # Forward pass: Apply the sign function
+// >>> y = torch.sign(x)
+// >>> print("Forward pass:")
+// Forward pass:
+// >>> print("x:", x)
+// x: tensor([-2., -1.,  0.,  1.,  2.], requires_grad=True)
+// >>> print("y:", y)
+// y: tensor([-1., -1.,  0.,  1.,  1.], grad_fn=<SignBackward0>)
+// >>> # Compute the loss (just an example)
+// >>> loss = y.sum()
+// >>> # Backward pass: Compute the gradients
+// >>> loss.backward()
+// >>> print("\nBackward pass:")
+// Backward pass:
+// >>> print("x.grad:", x.grad)
+// x.grad: tensor([0., 0., 0., 0., 0.])
+
+#[test]
+fn should_diff_sign() {
+    let data = TensorData::from([-2.0, -1.0, 0.0, 1.0, 2.0]);
+
+    let device = Default::default();
+    let x = TestAutodiffTensor::<1>::from_data(data, &device).require_grad();
+
+    let y = x.clone().sign();
+
+    let loss = y.clone().sum();
+    let grads = loss.backward();
+    let grad = x.grad(&grads).unwrap();
+
+    y.to_data()
+        .assert_eq(&TensorData::from([-1., -1., 0., 1., 1.]), false);
+    grad.to_data()
+        .assert_eq(&TensorData::from([0., 0., 0., 0., 0.]), false);
+}