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_polars/src/cloud/aws.rs

@@ -19,9 +19,7 @@ async fn aws_creds(aws_config: &SdkConfig) -> Result<Option<Credentials>, ShellE
                 error: format!(
                     "Could not fetch AWS credentials: {} - {}",
                     e,
-                    e.source()
-                        .map(|e| format!("{}", e))
-                        .unwrap_or("".to_string())
+                    e.source().map(|e| format!("{e}")).unwrap_or("".to_string())
                 ),
                 msg: "".into(),
                 span: None,

crates/nu_plugin_polars/src/dataframe/command/core/to_repr.rs

@@ -97,7 +97,7 @@ fn dataframe_command(
     input: Value,
 ) -> Result<PipelineData, ShellError> {
     let df = NuDataFrame::try_from_value_coerce(plugin, &input, call.head)?;
-    let value = Value::string(format!("{}", df), call.head);
+    let value = Value::string(format!("{df}"), call.head);
     Ok(PipelineData::Value(value, None))
 }
 

crates/nu_plugin_polars/src/dataframe/command/datetime/mod.rs

@@ -64,14 +64,14 @@ pub(crate) fn datetime_commands() -> Vec<Box<dyn PluginCommand<Plugin = PolarsPl
 pub fn timezone_from_str(zone_str: &str, span: Option<Span>) -> Result<TimeZone, ShellError> {
     TimeZone::opt_try_new(Some(PlSmallStr::from_str(zone_str)))
         .map_err(|e| ShellError::GenericError {
-            error: format!("Invalid timezone: {} : {}", zone_str, e),
+            error: format!("Invalid timezone: {zone_str} : {e}"),
             msg: "".into(),
             span,
             help: None,
             inner: vec![],
         })?
         .ok_or(ShellError::GenericError {
-            error: format!("Invalid timezone {}", zone_str),
+            error: format!("Invalid timezone {zone_str}"),
             msg: "".into(),
             span,
             help: None,

crates/nu_plugin_polars/src/main.rs

@@ -14,7 +14,7 @@ fn main() {
     match PolarsPlugin::new() {
         Ok(ref plugin) => serve_plugin(plugin, MsgPackSerializer {}),
         Err(e) => {
-            eprintln!("{}", e);
+            eprintln!("{e}");
             std::process::exit(1);
         }
     }