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/Cargo.toml

@@ -34,6 +34,7 @@ rust = {}
 
 [workspace.lints.clippy]
 expect_used = "deny"
+redundant_clone = "deny"
 uninlined_format_args = "deny"
 unwrap_used = "deny"