Remove preview labeling for uv 0.3.0 (#6166)

- Removes "experimental" labels from command documentation
- Removes preview warnings
- Removes `PreviewMode` from most structs and methods — we could keep it
around but I figure we can propagate it again easily where needed in the
future
- Enables preview behavior by default everywhere, e.g., `uv venv` will
download Python versions

crates/uv-python/Cargo.toml

@@ -22,7 +22,6 @@ platform-tags = { workspace = true }
 pypi-types = { workspace = true }
 uv-cache = { workspace = true }
 uv-client = { workspace = true }
-uv-configuration = { workspace = true }
 uv-extract = { workspace = true }
 uv-fs = { workspace = true }
 uv-state = { workspace = true }