Quaternion multiplication fix

[JalenLv]

Note that multiplying two numpy.ndarrays uses the broadcasting rule. To get quaternion product, we should multiply two Ratations

>>> x1
array([0., 1., 2., 3.])
>>> x2
array([0., 1., 2., 3.])
>>> x1 * x2
array([0., 1., 4., 9.])
>>> (R.from_quat(x1) * R.from_quat(x2)).as_quat()
array([-7.15302691e-18,  4.28571429e-01,  8.57142857e-01,  2.85714286e-01])

R.from_euler() creates a Rotation but the old code has another .as_quat() which converts a Rotation back to ndarray.

Ref:

• numpy.multiply
• Rotation
• as_quat
• from_euler
• from_quat