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/mktemp.rs

@@ -10,7 +10,7 @@ fn creates_temp_file() {
             "mktemp"
         );
         let loc = AbsolutePath::try_new(&output.out).unwrap();
-        println!("{:?}", loc);
+        println!("{loc:?}");
         assert!(loc.exists());
     })
 }