RFC: rm __array__, add __buffer__

[ev-br]

Try getting rid of __array__, replace with the buffer protocol's __buffer__.

cross-ref #67, #69

This does not seem to fix gh-102. scipy tests pass locally.
Replacing __array__ with __buffer__ makes code marginally simpler. Effectively bumps the python requirement to 3.12+ though.
So maybe this is a temp solution until dlpack matures.
¯\_(ツ)_/¯

[ev-br]

The matching SciPy PR: scipy/scipy#22189

[ev-br]

The current behavior: np.asarray(...) just works on python 3.12+, and errors out otherwise.
I'm going to merge this for the upcoming release, unless there are suggestions to the contrary.

On python 3.12:

In [3]: import sys; print(sys.version)
3.12.4 | packaged by conda-forge | (main, Jun 17 2024, 10:23:07) [GCC 12.3.0]

In [4]: np.array(xp.ones(3))
Out[4]: array([1., 1., 1.])

In [5]: np.ones(3) + xp.ones(3)     # can't do anything about
Out[5]: array([2., 2., 2.])

On python 3.11:

In [1]: import sys; print(sys.version)
3.11.0 | packaged by conda-forge | (main, Jan 14 2023, 12:27:40) [GCC 11.3.0]

In [2]: import array_api_strict as xp

In [3]: import numpy as np

In [4]: np.array(xp.ones(3))
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Cell In[4], line 1
----> 1 np.array(xp.ones(3))

File ~/repos/array-api-strict/array_api_strict/_array_object.py:170, in Array.__array__(self, *args, **kwds)
    168 def __array__(self, *args, **kwds):
    169     # a stub for python < 3.12; otherwise numpy silently produces object arrays
--> 170     raise TypeError(
    171         f"Interoperation with NumPy requires python >= 3.12. Please upgrade."
    172     )

TypeError: Interoperation with NumPy requires python >= 3.12. Please upgrade.

In [5]: xp.ones(3) + np.ones(3)
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Cell In[5], line 1
----> 1 xp.ones(3) + np.ones(3)

File ~/repos/array-api-strict/array_api_strict/_array_object.py:170, in Array.__array__(self, *args, **kwds)
    168 def __array__(self, *args, **kwds):
    169     # a stub for python < 3.12; otherwise numpy silently produces object arrays
--> 170     raise TypeError(
    171         f"Interoperation with NumPy requires python >= 3.12. Please upgrade."
    172     )

TypeError: Interoperation with NumPy requires python >= 3.12. Please upgrade.

[ev-br]

PSA: The timeline for this PR is "land in a couple of month's time". The current thinking is that short-term we work on the 2024.12 support in version 2.3, let the dust settle, and then merge this PR. Downstream testing with array-api-strict will then need to use python >= 3.12.