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-dev/src/build.rs

@@ -11,8 +11,8 @@ use uv_build::{SourceBuild, SourceBuildContext};
 use uv_cache::{Cache, CacheArgs};
 use uv_client::RegistryClientBuilder;
 use uv_configuration::{
-    BuildKind, BuildOptions, Concurrency, ConfigSettings, IndexStrategy, PreviewMode,
-    SetupPyStrategy, SourceStrategy,
+    BuildKind, BuildOptions, Concurrency, ConfigSettings, IndexStrategy, SetupPyStrategy,
+    SourceStrategy,
 };
 use uv_dispatch::BuildDispatch;
 use uv_git::GitResolver;
@@ -96,7 +96,6 @@ pub(crate) async fn build(args: BuildArgs) -> Result<PathBuf> {
         exclude_newer,
         sources,
         concurrency,
-        PreviewMode::Enabled,
     );
 
     let builder = SourceBuild::setup(