fix img_path is not Path

lec2note/processing/processor.py

@@ -23,6 +23,7 @@ class Processor:  # noqa: D101
 
     @staticmethod
     def _img_to_data_uri(img_path: Path) -> str:
+        img_path = Path(img_path)
         mime, _ = mimetypes.guess_type(img_path)
         b64 = base64.b64encode(img_path.read_bytes()).decode()
         return f"data:{mime};base64,{b64}"