fix: address ty complaint

src/heretic/model.py

@@ -743,7 +743,12 @@ class Model:
             max_new_tokens=4096,
         )  # ty:ignore[call-non-callable]
 
-        return self.tokenizer.decode(
-            outputs[0, inputs["input_ids"].shape[1] :],
-            skip_special_tokens=True,
+        # This cast is valid because str is the return type
+        # when passing a sequence of token IDs.
+        return cast(
+            str,
+            self.tokenizer.decode(
+                outputs[0, inputs["input_ids"].shape[1] :],
+                skip_special_tokens=True,
+            ),
         )