Set attributes from new state before on_step.

def _prepare_step(self, state):
        """Set attributes from new state before on_step."""
        self.state: GameState = state
        # Required for events
        self._units_previous_map.clear()
        for unit in self.units:
            self._units_previous_map[unit.tag] = unit

        self.units: Units = state.own_units
        self.workers: Units = self.units(race_worker[self.race])
        self.townhalls: Units = self.units(race_townhalls[self.race])
        self.geysers: Units = self.units(race_gas[self.race])

        self.minerals: Union[float, int] = state.common.minerals
        self.vespene: Union[float, int] = state.common.vespene
        self.supply_used: Union[float, int] = state.common.food_used
        self.supply_cap: Union[float, int] = state.common.food_cap
        self.supply_left: Union[float, int] = self.supply_cap - self.supply_used
        # reset cached values
        self.cached_known_enemy_structures = None
        self.cached_known_enemy_units = None