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/core/src/turn_diff_tracker.rs

@@ -678,7 +678,7 @@ index {left_oid}..{right_oid}
         let dest = dir.path().join("dest.txt");
         let mut acc = TurnDiffTracker::new();
         let mv = HashMap::from([(
-            src.clone(),
+            src,
             FileChange::Update {
                 unified_diff: "".into(),
                 move_path: Some(dest.clone()),