Use np.int8 instead of np.int64 for action mask dtype

This is more memory sufficient for only 0-1's.
And seems to be the standard for action mask at least for ray.rllib,
as shown in `action_mask_key` documentation at
https://docs.ray.io/en/latest/rllib/rllib-training.html

skdecide/builders/domain/events.py

@@ -384,7 +384,7 @@ def _get_action_mask(
                     1 if applicable_actions.contains(a) else 0
                     for a in action_space.get_elements()
                 ],
-                dtype=np.int64,
+                dtype=np.int8,
             )
         else:
             # multi agent
@@ -394,7 +394,7 @@ def _get_action_mask(
                         1 if agent_applicable_actions.contains(a) else 0
                         for a in action_space[agent].get_elements()
                     ],
-                    dtype=np.int64,
+                    dtype=np.int8,
                 )
                 for agent, agent_applicable_actions in applicable_actions.items()
             }

skdecide/core.py

@@ -672,7 +672,7 @@ def cast_evaluate_function(memory, action, next_state):
 # The following alias is needed in core module so that autocast works:
 #  - `autocast` does not like "." after strings other than "D",
 #  - `autocast` needs types in annotations to be evaluable in `skdecide.core` namespace.
-Mask = npt.NDArray[np.int64]
+Mask = npt.NDArray[np.int8]
 """Alias for single agent action mask."""
 
 

skdecide/hub/solver/ray_rllib/ray_rllib.py

@@ -324,7 +324,7 @@ def _init_algo(self) -> None:
                             0,
                             1,
                             shape=(len(self._wrapped_action_space[k].get_elements()),),
-                            dtype=np.int64,
+                            dtype=np.int8,
                         ),
                     }
                 )
@@ -539,7 +539,7 @@ def __init__(
                                             self._wrapped_action_space[k].get_elements()
                                         ),
                                     ),
-                                    dtype=np.int64,
+                                    dtype=np.int8,
                                 ),
                             }
                         )
@@ -569,7 +569,7 @@ def __init__(
                                             self._wrapped_action_space[k].get_elements()
                                         ),
                                     ),
-                                    dtype=np.int64,
+                                    dtype=np.int8,
                                 ),
                             }
                         )