style: fix formatting for rustfmt compliance

- Add trailing newlines to all source files
- Remove extra blank lines
- Simplify closure formatting in benchmarks

examples/benchmark_single.rs

@@ -33,4 +33,5 @@ fn main() {
             std::process::exit(1);
         }
     }
-}
+}
+

examples/parse.rs

@@ -19,4 +19,5 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
     println!("  Units: {}", doc.units.len());
 
     Ok(())
-}
+}
+

examples/validate.rs

@@ -26,4 +26,5 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
     }
 
     Ok(())
-}
+}
+