don't use partial in type hint, due to lack of support

src/justcause/data/frames.py

@@ -70,7 +70,7 @@ def __init__(self, data, *args, **kwargs):
  self._names = dict(covariates=covariates)
 
  @property
- def _constructor(self) -> partial["CausalFrame"]:
+ def _constructor(self) -> "CausalFrame":
  # This is called during operations with CausalFrames
  # We pass a marker to differentiate between explicit and implicit invocation
  kwargs = {"_internal_operation": True, **self._names}