Fix old checkpoint deletion by sorting the models properly

Should fix voicepaw#65 this time around.
The reason why this didn't work before is because it sorted them based on their name or time alone, but not also based on their prefix, so the resulting array looked like "G_", "D_", "G_", "D_", ...

This addresses that by also sorting based on their prefix, resulting in a properly sorted array "G_", "G_", "G_", "D_", "D_", "D_"

This has to be done this way due to how the itertools.groupby method works: https://note.nkmk.me/en/python-itertools-groupby/

src/so_vits_svc_fork/utils.py

@@ -451,24 +451,26 @@ def clean_checkpoints(
     sort_by_time      --  True -> chronologically delete ckpts
                           False -> lexicographically delete ckpts
     """
+    LOG.warning("Cleaning old checkpoints...")
     path_to_models = Path(path_to_models)
-    name_key = lambda p: int(re.match(r"._(\d+)", p.stem).group(1))
+
+    # Define sort key functions
+    name_key = lambda p: int(re.match(r"[GD]_(\d+)\.pth", p.name).group(1))
     time_key = lambda p: p.stat().st_mtime
-    models_sorted = sorted(
-        filter(
-            lambda p: (p.is_file() and re.match(r"._\d+", p.stem)),
-            path_to_models.glob("*.pth"),
-        ),
-        key=time_key if sort_by_time else name_key,
-    )
-    models_sorted_grouped = groupby(models_sorted, lambda p: p.stem[0])
-    for k, g in models_sorted_grouped:
-        to_dels = list(g)[:-n_ckpts_to_keep]
-        for to_del in to_dels:
-            if to_del.stem.endswith("_0"):
-                continue
-            LOG.warning(f"Removing {to_del}")
-            to_del.unlink()
+    path_key = lambda p: (p.name[0],) + (time_key(p),) if sort_by_time else (p.name[0],) + (name_key(p),)
+
+    models = list(filter(lambda p: (p.is_file() and re.match(r"[GD]_\d+\.pth", p.name) and not p.name.endswith("_0.pth")), path_to_models.glob("*.pth")))
+
+    models_sorted = sorted(models, key=path_key)
+
+    models_sorted_grouped = groupby(models_sorted, lambda p: p.name[0])
+
+    for group_name, group_items in models_sorted_grouped:
+        to_delete_list = list(group_items)[:-n_ckpts_to_keep]
+
+        for to_delete in to_delete_list:
+            LOG.warning(f"Removing {to_delete}")
+            to_delete.unlink()
 
 
 def summarize(