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/environment_context.rs

@@ -63,7 +63,7 @@ impl EnvironmentContext {
                     if writable_roots.is_empty() {
                         None
                     } else {
-                        Some(writable_roots.clone())
+                        Some(writable_roots)
                     }
                 }
                 _ => None,