keras/src/optimizers/lion.py/Lion/build
class Lion:    def build(self, var_list):
        """Initialize optimizer variables.

        Lion optimizer has one variable `momentums`.

        Args:
            var_list: list of model variables to build Lion variables on.
        """
        if self.built:
            return
        super().build(var_list)
        self._momentums = []
        for var in var_list:
            self._momentums.append(
                self.add_variable_from_reference(
                    reference_variable=var, name="momentum"
                )
            )