Update Rust toolchain to 1.91 and MSRV to 1.89 (#16531)

## Summary

Updates Rust Toolchain to
[1.91](https://blog.rust-lang.org/2025/10/30/Rust-1.91.0/) and bumps
MSRV to [1.89](https://blog.rust-lang.org/2025/08/07/Rust-1.89.0/) per
versioning policy. New clippy rule [implicit
clone](https://rust-lang.github.io/rust-clippy/master/index.html#implicit_clone)
resulted in some minor changes (some with improvements).

Updates trampoline to `nightly-2025-06-23` which is roughly 1.89~. The
trampoline binaries do not need to be regenerated as there should be no
changes.

crates/uv-dev/src/generate_options_reference.rs

@@ -169,7 +169,7 @@ fn generate_set(output: &mut String, set: Set, parents: &mut Vec<Set>) {
         generate_set(
             output,
             Set::Named {
-                name: set_name.to_string(),
+                name: set_name.to_owned(),
                 set: *sub_set,
             },
             parents,