Rotate vector by angle in radians.

def rot_rads_v2(vec_a, rads):
    """ Rotate vector by angle in radians."""

    x = vec_a.x * math.cos(rads) - vec_a.y * math.sin(rads)
    y = vec_a.x * math.sin(rads) + vec_a.y * math.cos(rads)
    return Vec2(x, y)