fix: unique weight saver

homura/callbacks.py

@@ -165,8 +165,8 @@ def __init__(self, *callbacks: Iterable[Callback] or Callback):
  if not isinstance(callbacks, Iterable):
  callbacks = [callbacks]
 
- for c in callbacks:
- if c is not None and not isinstance(c, Callback):
+ for c in [c for c in callbacks if c is not None]:
+ if isinstance(c, Callback):
  raise TypeError(f"{c} is not a callback!")
  self._callbacks: Iterable[Callback] = list(callbacks)