Avoid iterating over the config file twice

aeon/io/reader.py

@@ -353,7 +353,7 @@ def read(self, file: Path) -> pd.DataFrame:
             parts = unique_parts
 
         # Set new columns, and reformat `data`.
-        data = self.class_int2str(data, config_file)
+        data = self.class_int2str(data, identities)
         n_parts = len(parts)
         part_data_list = [pd.DataFrame()] * n_parts
         new_columns = pd.Series(["identity", "identity_likelihood", "part", "x", "y", "part_likelihood"])
@@ -410,18 +410,10 @@ def get_bodyparts(config_file: Path) -> list[str]:
         return parts
 
     @staticmethod
-    def class_int2str(data: pd.DataFrame, config_file: Path) -> pd.DataFrame:
+    def class_int2str(data: pd.DataFrame, classes: list[str]) -> pd.DataFrame:
         """Converts a class integer in a tracking data dataframe to its associated string (subject id)."""
-        if config_file.stem == "confmap_config":  # SLEAP
-            with open(config_file) as f:
-                config = json.load(f)
-            try:
-                heads = config["model"]["heads"]
-                classes = util.find_nested_key(heads, "classes")
-            except KeyError as err:
-                raise KeyError(f"Cannot find classes in {config_file}.") from err
-            for i, subj in enumerate(classes):
-                data.loc[data["identity"] == i, "identity"] = subj
+        for i, subj in enumerate(classes):
+            data.loc[data["identity"] == i, "identity"] = subj
         return data
 
     @classmethod