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()
     }
 

crates/uv-python/src/interpreter.rs

@@ -567,7 +567,7 @@ impl Interpreter {
     ///
     /// 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>> {
         let target = self.target().map(Target::site_packages);
 
         let prefix = self

crates/uv-python/src/sysconfig/parser.rs

@@ -22,7 +22,7 @@ pub(super) struct SysconfigData(BTreeMap<String, Value>);
 
 impl SysconfigData {
     /// Returns an iterator over the key-value pairs in the map.
-    pub(super) fn iter_mut(&mut self) -> std::collections::btree_map::IterMut<String, Value> {
+    pub(super) fn iter_mut(&mut self) -> std::collections::btree_map::IterMut<'_, String, Value> {
         self.0.iter_mut()
     }