chore: Simplify newtype to tuple struct

benches/threading.rs

@@ -56,7 +56,7 @@ pub fn process_multi_threaded_german(
                     // }
 
                     let stage = GermanStage;
-                    let result = stage.substitute(&item).unwrap();
+                    let result: String = stage.substitute(&item).unwrap().into();
 
                     let mut results = results_clone.lock().unwrap();
                     info!("Thread {} finished processing line", i);
@@ -73,7 +73,7 @@ pub fn process_multi_threaded_german(
     let mut results = Arc::try_unwrap(results).unwrap().into_inner().unwrap();
     results.sort_by_key(|&(index, _)| index);
 
-    let results: Vec<String> = results.into_iter().map(|(_, result)| result.0).collect();
+    let results: Vec<String> = results.into_iter().map(|(_, result)| result).collect();
 
     destination.write_all(results.join("\n").as_bytes())
 }

src/stages/german/driver.rs

@@ -566,8 +566,8 @@ mod tests {
             word: String
         ) (|data: &TestProcess| {
                 let input = word.clone();
-                let result = GermanStage{}.substitute(&input).unwrap();
-                insta::assert_yaml_snapshot!(data.to_string(), result.0);
+                let result: String = GermanStage{}.substitute(&input).unwrap().into();
+                insta::assert_yaml_snapshot!(data.to_string(), result);
             }
         )
     }

src/stages/tooling.rs

@@ -24,10 +24,7 @@ impl std::fmt::Display for StageError {
 /// [newtype](https://doc.rust-lang.org/rust-by-example/generics/new_types.html), used
 /// for increased clarity.
 #[derive(Debug)]
-pub struct SubstitutedString(
-    /// The actual string contents.
-    pub String,
-);
+pub struct SubstitutedString(String);
 
 /// Convert a [`SubstitutedString`] into a [`String`].
 ///