fix: cosine similarity throws when vectors unequal lengths

Author: jpohhhh

lib/extensions/vector.dart

@@ -3,6 +3,10 @@ import 'package:ml_linalg/vector.dart';
 
 extension Similarity on Vector {
   double cosineSimilarity(Vector vector) {
+    if (length != vector.length) {
+      print('Fonnx.Vector.Similarity.cosineSimilarity: Vectors must have the same length. A vector has length $length, while the other has length ${vector.length}. Returning 0 for similarity.');
+      return 0.0;
+    }
     final distance = distanceTo(vector, distance: Distance.cosine);
     return 1.0 - distance;
   }