feat: add is_empty method to GitIndexCache and refactor Hungarian algorithm loop

- Introduced `is_empty` method in `GitIndexCache` to check if the cache has any entries.
- Refactored the loop in the `min_cost_assignment` function in `hungarian.rs` to use `enumerate` for improved readability and efficiency.

src/git.rs

@@ -306,6 +306,10 @@ impl GitIndexCache {
         self.entries.len()
     }
 
+    pub fn is_empty(&self) -> bool {
+        self.entries.is_empty()
+    }
+
     /// Returns `true` if the new content's blob SHA1 matches the git index
     /// entry for this path, meaning the file on disk almost certainly
     /// already has this content.

src/hungarian.rs

@@ -94,9 +94,9 @@ pub fn min_cost_assignment(
     }
 
     let mut result = Vec::with_capacity(rows.min(cols));
-    for j in 1..=n {
+    for (j, &assigned_row) in p.iter().enumerate().skip(1) {
-        if p[j] != 0 && p[j] <= rows && j <= cols {
+        if assigned_row != 0 && assigned_row <= rows && j <= cols {
-            result.push((p[j] - 1, j - 1));
+            result.push((assigned_row - 1, j - 1));
         }
     }
     result