fix: dataclass backwards compatibility

lstm/model_state.py

@@ -1,12 +1,20 @@
 from __future__ import annotations
 
+import sys
 import typing
 from dataclasses import dataclass
 
 import numpy.typing as npt
 
+# `slots` feature added to of `dataclass` in 3.10
+# see: https://docs.python.org/3.12/library/dataclasses.html#dataclasses.dataclass
+if sys.version_info < (3, 10):
+    dataclass_kwargs = {}
+else:
+    dataclass_kwargs = {"slots": True}
 
-@dataclass(slots=True)
+
+@dataclass(**dataclass_kwargs)
 class Var:
     """
     State variable representation.