fix: replace mutable default arguments in trainer.py

Using mutable default arguments (e.g. `= []`) in Python function
signatures is a well-known anti-pattern (W0102). The default list is
shared across all calls, which can lead to unexpected behavior if the
list is ever mutated in place.

Replace `= []` with `= None` and add explicit `None` guards for
`__move_components_to_device` and `__move_components_to_cpu`.

finetune/trainer.py

@@ -713,7 +713,9 @@ class Trainer:
         else:
             raise ValueError(f"Invalid mixed precision: {self.args.mixed_precision}")
 
-    def __move_components_to_device(self, dtype, ignore_list: List[str] = []):
+    def __move_components_to_device(self, dtype, ignore_list: List[str] = None):
+        if ignore_list is None:
+            ignore_list = []
         ignore_list = set(ignore_list)
         components = self.components.model_dump()
         for name, component in components.items():
@@ -723,7 +725,9 @@ class Trainer:
                         self.components, name, component.to(self.accelerator.device, dtype=dtype)
                     )
 
-    def __move_components_to_cpu(self, unload_list: List[str] = []):
+    def __move_components_to_cpu(self, unload_list: List[str] = None):
+        if unload_list is None:
+            unload_list = []
         unload_list = set(unload_list)
         components = self.components.model_dump()
         for name, component in components.items():