chore: enable clippy::redundant_clone (#3489)

Created this PR by:

- adding `redundant_clone` to `[workspace.lints.clippy]` in
`cargo-rs/Cargol.toml`
- running `cargo clippy --tests --fix`
- running `just fmt`

Though I had to clean up one instance of the following that resulted:

```rust
let codex = codex;
```

codex-rs/tui/src/onboarding/auth.rs

@@ -432,7 +432,7 @@ impl AuthModeWidget {
         match &mut *guard {
             SignInState::ApiKeyEntry(state) => {
                 if state.value.is_empty() {
-                    if let Some(prefill) = prefill_from_env.clone() {
+                    if let Some(prefill) = prefill_from_env {
                         state.value = prefill;
                         state.prepopulated_from_env = true;
                     } else {