Apply more recent/nightly clippy lints (#7916)

# Description

- Use inline format strings in dataframe code
- Fix manual `.is_ascii_digit()` check
- Remove unnecessary `.into_iter()` calls

crates/nu-command/src/date/list_timezone.rs

@@ -46,7 +46,6 @@ impl Command for SubCommand {
                 }];
                 Value::Record { cols, vals, span }
             })
-            .into_iter()
             .into_pipeline_data(engine_state.ctrlc.clone()))
     }