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/shell.rs

@@ -326,10 +326,7 @@ mod tests {
                 .format_default_shell_invocation(input.iter().map(|s| s.to_string()).collect());
             let expected_cmd = expected_cmd
                 .iter()
-                .map(|s| {
-                    s.replace("BASHRC_PATH", bashrc_path.to_str().unwrap())
-                        .to_string()
-                })
+                .map(|s| s.replace("BASHRC_PATH", bashrc_path.to_str().unwrap()))
                 .collect();
 
             assert_eq!(actual_cmd, Some(expected_cmd));
@@ -435,10 +432,7 @@ mod macos_tests {
                 .format_default_shell_invocation(input.iter().map(|s| s.to_string()).collect());
             let expected_cmd = expected_cmd
                 .iter()
-                .map(|s| {
-                    s.replace("ZSHRC_PATH", zshrc_path.to_str().unwrap())
-                        .to_string()
-                })
+                .map(|s| s.replace("ZSHRC_PATH", zshrc_path.to_str().unwrap()))
                 .collect();
 
             assert_eq!(actual_cmd, Some(expected_cmd));