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/safety.rs

@@ -293,7 +293,7 @@ mod tests {
         // With the parent dir explicitly added as a writable root, the
         // outside write should be permitted.
         let policy_with_parent = SandboxPolicy::WorkspaceWrite {
-            writable_roots: vec![parent.clone()],
+            writable_roots: vec![parent],
             network_access: false,
             exclude_tmpdir_env_var: true,
             exclude_slash_tmp: true,