[Demucs to Safetensors] Run without demucs lib

Even when we didn't use the lib the torch.load needed it to map
the classes during the pickle load.
So now we remap the lib modules to our own copy of the classes.

tool/demucs2safetensors.py

@@ -7,6 +7,7 @@
 # python tool/tool/demucs2safetensors.py --yaml DEMUCS.YAML
 # You must manually download the .th files and copy them to the YAML dir
 # First version by Gemini 2.5 Pro
+from contextlib import contextmanager
 from copy import deepcopy
 import argparse
 import json
@@ -28,9 +29,38 @@ from source.utils.misc import cli_add_verbose, FractionEncoder
 from source.utils.logger import main_logger, logger_set_standalone
 from source.db.models_db import cli_add_db, get_download_url, ModelsDB
 from source.db.hash import get_hash
+import source.inference.Demucs as local_demucs_module
+import source.inference.HDemucs as local_hdemucs_module
+import source.inference.HTDemucs as local_htdemucs_module
+MODULES_MAP = {'demucs': local_demucs_module,
+               'demucs.demucs': local_demucs_module,
+               'demucs.hdemucs': local_hdemucs_module,
+               'demucs.htdemucs': local_htdemucs_module}
 logger = main_logger
 
 
+@contextmanager
+def remap_module(modules_map):
+    """
+    A context manager to temporarily remap an old module name to a new one.
+    This is useful for loading pickled objects that depend on old paths.
+    """
+    original_modules = {}
+    for old_name, new_module in modules_map.items():
+        original_modules[old_name] = sys.modules.get(old_name)
+        sys.modules[old_name] = new_module
+    try:
+        yield
+    finally:
+        # Restore the original state
+        for old_name, original_module in original_modules.items():
+            if original_module is not None:
+                sys.modules[old_name] = original_module
+            else:
+                # If the module wasn't there before, remove our patch
+                del sys.modules[old_name]
+
+
 def convert_demucs_model(yaml_path_str: str, model_paths: list[str], output_path_str: str, all_metadata, data: Dict):
     """
     Loads an original Demucs model bag, extracts weights and all necessary metadata
@@ -76,8 +106,10 @@ def convert_demucs_model(yaml_path_str: str, model_paths: list[str], output_path
         path = model_file_map[sig]
         main_logger.info(f"\n- Processing model '{sig}' from '{path.name}'...")
 
-        # This is the only "unsafe" part, loading the original pickle file
-        pkg = torch.load(path, map_location='cpu', weights_only=False)
+        # Use the context manager to perform the remap
+        with remap_module(MODULES_MAP):
+            # This is the only "unsafe" part, loading the original pickle file
+            pkg = torch.load(path, map_location='cpu', weights_only=False)
 
         klass, args, kwargs, state = pkg["klass"], pkg["args"], pkg["kwargs"], pkg["state"]
         main_logger.info(f"  - Model class: {klass.__module__}.{klass.__name__}")