Update Rust toolchain to 1.89 (#15157)

## Summary

Bumps Rust toolchain to 1.89, but not the MSRV.

Lifetime changes is related to a new lint rule explained in
https://blog.rust-lang.org/2025/08/07/Rust-1.89.0/#mismatched-lifetime-syntaxes-lint

## Test Plan

Existing Tests

crates/uv-python/src/environment.rs

@@ -302,7 +302,7 @@ impl PythonEnvironment {
     ///
     /// Some distributions also create symbolic links from `purelib` to `platlib`; in such cases, we
     /// still deduplicate the entries, returning a single path.
-    pub fn site_packages(&self) -> impl Iterator<Item = Cow<Path>> {
+    pub fn site_packages(&self) -> impl Iterator<Item = Cow<'_, Path>> {
         self.0.interpreter.site_packages()
     }