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/seatbelt.rs

@@ -153,7 +153,7 @@ mod tests {
         // Build a policy that only includes the two test roots as writable and
         // does not automatically include defaults TMPDIR or /tmp.
         let policy = SandboxPolicy::WorkspaceWrite {
-            writable_roots: vec![root_with_git.clone(), root_without_git.clone()],
+            writable_roots: vec![root_with_git, root_without_git],
             network_access: false,
             exclude_tmpdir_env_var: true,
             exclude_slash_tmp: true,