Implement consistent `__setitem__` between `numpy/cupy.ndarray`s and `VirtualArray`s

[ikrommyd]

Right now VirtualArray_instance[slice] = Other_VirtualArray_instance works but it's not clear to me why.
Also numpy.ndarray_instance[slice] = VirtualArray_instance works but not cupy.ndarray_instance[slice] = VirtualArray_instance. The latter fails with

File cupy/_core/core.pyx:1641, in cupy._core.core._ndarray_base.__setitem__()

File cupy/_core/_routines_indexing.pyx:51, in cupy._core._routines_indexing._ndarray_setitem()

File cupy/_core/_routines_indexing.pyx:1017, in cupy._core._routines_indexing._scatter_op()

File cupy/_core/core.pyx:789, in cupy._core.core._ndarray_base.fill()

File cupy/_core/core.pyx:1293, in cupy._core.core._ndarray_base.__nonzero__()

ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

see cupy/cupy#9089.

All that should be made more consistent because it's used in the codebase like offsets[:-1] = starts for example and offsets and starts can be either np/cp.ndarray or VirtualArray in such cases.