chore: use inline formatting

Minor cleanup using clippy autofix.  This makes the code a bit more readable, and helps spot a few inefficiencies and possible bugs.

```
cargo clippy --fix --workspace -- -A clippy::all -W clippy::uninlined_format_args && cargo fmt
```

tests/by-util/test_cp.rs

@@ -6093,9 +6093,7 @@ fn test_cp_preserve_xattr_readonly_source() {
     let stdout = String::from_utf8_lossy(&getfattr_output.stdout);
     assert!(
         stdout.contains(xattr_key),
-        "Expected '{}' not found in getfattr output:\n{}",
-        xattr_key,
-        stdout
+        "Expected '{xattr_key}' not found in getfattr output:\n{stdout}"
     );
 
     at.set_readonly(source_file);