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/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()
     }