style: final formatting fixes for rustfmt

- Remove trailing whitespace
- Add newlines at end of files
- Fix multi-line string formatting

src/bin/crabrl_bench.rs

@@ -38,3 +38,4 @@ fn main() {
     }
 }
 
+

src/model.rs

@@ -349,3 +349,4 @@ impl Document {
 }
 
 
+