perf: use Arc<str> for diffs and Arc<PathBuf> for git fetch

Change FileChange::diff from Arc<String> to Arc<str>, saving
8 bytes per FileChange (16 vs 24 byte fat pointer). Share
work_dir via Arc<PathBuf> in fetch_file_contents instead of
cloning PathBuf per spawned task.

Author: Sephyi

src/services/git.rs

@@ -122,7 +122,7 @@ impl GitService {
             files.push(FileChange {
                 path: file_path,
                 status,
-                diff: Arc::new(diff),
+                diff: Arc::from(diff),
                 additions,
                 deletions,
                 category,
@@ -194,9 +194,10 @@ impl GitService {
         paths: &[PathBuf],
     ) -> (HashMap<PathBuf, String>, HashMap<PathBuf, String>) {
         let mut set = tokio::task::JoinSet::new();
+        let work_dir: Arc<PathBuf> = Arc::new(self.work_dir.clone());
 
         for path in paths {
-            let work_dir = self.work_dir.clone();
+            let work_dir = Arc::clone(&work_dir);
             let path = path.clone();
             set.spawn(async move {
                 let staged =

tests/analyzer.rs

@@ -15,7 +15,7 @@ fn make_file_change(path: &str, diff: &str, additions: usize, deletions: usize)
     FileChange {
         path: PathBuf::from(path),
         status: ChangeStatus::Added,
-        diff: Arc::new(diff.to_string()),
+        diff: Arc::from(diff),
         additions,
         deletions,
         category: FileCategory::from_path(&PathBuf::from(path)),

tests/helpers.rs

@@ -19,7 +19,7 @@ pub fn make_file_change(
     FileChange {
         path: PathBuf::from(path),
         status,
-        diff: Arc::new(diff.to_string()),
+        diff: Arc::from(diff),
         additions,
         deletions,
         category: FileCategory::from_path(&PathBuf::from(path)),