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-autodiff/Cargo.toml

@@ -0,0 +1,45 @@
+[package]
+authors = ["nathanielsimard <nathaniel.simard.42@gmail.com>"]
+categories = ["science"]
+description = "Automatic differentiation backend for the Burn framework"
+edition.workspace = true
+keywords = ["deep-learning", "machine-learning", "data"]
+license.workspace = true
+name = "burn-autodiff"
+readme.workspace = true
+repository = "https://github.com/tracel-ai/burn/tree/main/crates/burn-autodiff"
+documentation = "https://docs.rs/burn-autodiff"
+version.workspace = true
+
+[lints]
+workspace = true
+
+[features]
+default = ["std", "tracing"]
+std = ["dep:parking_lot"]
+export_tests = []         # check checkpointer is_empty in tests
+
+tracing = [
+    "dep:tracing",
+    "burn-std/tracing",
+    "burn-backend/tracing",
+]
+
+[dependencies]
+burn-std = { path = "../burn-std", version = "=0.21.0-pre.2", default-features = false }
+burn-backend = { path = "../burn-backend", version = "=0.21.0-pre.2", default-features = false }
+
+
+derive-new = { workspace = true }
+spin = { workspace = true }
+parking_lot = { workspace = true, optional = true }
+log = { workspace = true }
+hashbrown = { workspace = true }
+num-traits = { workspace = true }
+portable-atomic = { workspace = true }
+tracing = { workspace = true, optional = true, features = ["default"] }
+
+
+[package.metadata.docs.rs]
+features = ["default"]
+rustdoc-args = ["--cfg", "docsrs"]