Fix easy clippy lints from latest stable (#16053)

1.88.0 was released today, clippy now lints (machine-applicable)
against:
- format strings with empty braces that could be inlined
  - easy win
- `manual_abs_diff`
- returning of a stored result of the last expression.
  - this can be somewhat contentious but touched only a few places

crates/nu-command/tests/commands/utouch.rs

@@ -540,10 +540,7 @@ fn change_file_times_to_date() {
         assert!(
             got_atime.signed_duration_since(expected).lt(&threshold)
                 && got_mtime.signed_duration_since(expected).lt(&threshold),
-            "Expected: {}. Got: atime={}, mtime={}",
-            expected,
-            got_atime,
-            got_mtime
+            "Expected: {expected}. Got: atime={got_atime}, mtime={got_mtime}"
         );
         assert!(got_mtime.signed_duration_since(expected).lt(&threshold));
     })