Extend SAPYB to array multiplication

[MargaretDuff]

Description

E.g. in SPDHG the line self.x.sapyb(1., self._zbar, -self._tau, out=self._x_tmp), if self._tau is an array then -self._tau assigns another array, with increased memory usage.

Something that implements z = a * a_arr * x + b * b_arr * y efficiently will add more flexibility

[MargaretDuff]

SANYB?