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/gelu.rs

@@ -0,0 +1,29 @@
+use super::*;
+use burn_tensor::{TensorData, Tolerance, activation};
+
+#[test]
+fn should_diff_gelu() {
+    let device = Default::default();
+    let tensor_1 =
+        TestAutodiffTensor::<2>::from_floats([[0.0, 1.0], [-3.0, 4.0]], &device).require_grad();
+    let tensor_2 =
+        TestAutodiffTensor::from_floats([[6.0, -0.5], [9.0, 10.0]], &device).require_grad();
+
+    let x = tensor_1.clone().matmul(activation::gelu(tensor_2.clone()));
+    let x = tensor_1.clone().matmul(x);
+    let grads = x.backward();
+
+    let grad_1 = tensor_1.grad(&grads).unwrap();
+    let grad_2 = tensor_2.grad(&grads).unwrap();
+
+    let tolerance = Tolerance::permissive();
+    let expected = TensorData::from([[1.46281, 1.46281], [48.22866, 153.46280]]);
+    grad_1
+        .to_data()
+        .assert_approx_eq::<FloatElem>(&expected, tolerance);
+
+    let expected = TensorData::from([[-15.0000, -1.98757], [17.0000, 17.0000]]);
+    grad_2
+        .to_data()
+        .assert_approx_eq::<FloatElem>(&expected, tolerance);
+}