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-plugin/src/plugin/mod.rs

@@ -663,7 +663,7 @@ fn print_help(plugin: &impl Plugin, encoder: impl PluginEncoder) {
         .as_ref()
         .map(|stem| stem.to_string_lossy().into_owned())
         .unwrap_or_else(|| "(unknown)".into());
-    println!("Plugin file path: {}", plugin_name);
+    println!("Plugin file path: {plugin_name}");
 
     let mut help = String::new();
     let help_style = HelpStyle::default();
@@ -685,7 +685,7 @@ fn print_help(plugin: &impl Plugin, encoder: impl PluginEncoder) {
             })
             .and_then(|_| {
                 let flags = get_flags_section(&signature, &help_style, |v| match v {
-                    FormatterValue::DefaultValue(value) => format!("{:#?}", value),
+                    FormatterValue::DefaultValue(value) => format!("{value:#?}"),
                     FormatterValue::CodeString(text) => text.to_string(),
                 });
                 write!(help, "{flags}")