Move preview features into a dedicated crate (#15482)

## Summary

This is causing some cyclic dependencies issues for me, because these
can be used in virtually _any_ crate (like `uv-install-wheel`), which
then means that all of `uv-configuration` becomes a dependency, etc. I
think this should be a leaf crate so that we can safely depend on it
anywhere.

crates/uv-python/src/environment.rs

@@ -7,9 +7,9 @@ use owo_colors::OwoColorize;
 use tracing::debug;
 
 use uv_cache::Cache;
-use uv_configuration::Preview;
 use uv_fs::{LockedFile, Simplified};
 use uv_pep440::Version;
+use uv_preview::Preview;
 
 use crate::discovery::find_python_installation;
 use crate::installation::PythonInstallation;