This PR adds JAX as a new nplike

[sw5sh]

No description provided.

[codecov]

Codecov Report

Merging #1399 (d0d7b9c) into main (edfce38) will decrease coverage by 0.07%.
The diff coverage is 31.29%.

Impacted Files	Coverage Δ
src/awkward/_v2/_connect/cuda/__init__.py	0.00% <0.00%> (ø)
src/awkward/_v2/_connect/jax/__init__.py	0.00% <0.00%> (ø)
src/awkward/_v2/operations/convert/ak_from_cupy.py	50.00% <0.00%> (+23.33%)	⬆️
src/awkward/_v2/operations/convert/ak_from_jax.py	50.00% <0.00%> (-25.00%)	⬇️
src/awkward/_v2/operations/convert/ak_to_cupy.py	33.33% <0.00%> (+23.95%)	⬆️
src/awkward/_v2/operations/convert/ak_to_jax.py	33.33% <0.00%> (-41.67%)	⬇️
src/awkward/_v2/operations/describe/ak_backend.py	10.00% <0.00%> (-2.50%)	⬇️
src/awkward/_v2/_util.py	75.11% <37.06%> (-8.22%)	⬇️
src/awkward/_v2/contents/numpyarray.py	90.42% <50.00%> (-0.15%)	⬇️
...rc/awkward/_v2/operations/convert/ak_from_numpy.py	100.00% <100.00%> (+27.77%)	⬆️
... and 1 more

[jpivarski]

Thanks for this!

Some large-scale refactoring things:

• The Jax nplike is not much different from the Cupy one, and the Cupy one is in the ak.nplike module. I think the Jax one could go here (and it needs to be possible to declare the class without importing jax. Whenever you have something that depends on two attributes, like "is an nplike" and "is for JAX", there's always a question of whether to organize them such that all the nplikes are together or to organize them such that all the JAX-related stuff is together. Let's organize it with all nplikes together, because that will enforce that they behave the same way with respect to when the third-party library gets imported. Some nplikes, like the TypeTracer, are in other places, but that's because the TypeTracer is very different from the nplikes for third-party libraries.
• Modules in ak._v2.operations.*.* should each provide one high-level function. See, for instance, ak_from_parquet and ak_metadata_from_parquet. There's a lot of overlap between these two, but they're in separate files to maintain that structure. So please split ak_from_lib back into ak_from_cupy and ak_from_jax (same for the "to" direction).
• Sharing code in the implementations of from_X and to_X is a good idea, and maybe it would be possible to extend this shared code to NumPy as well as CuPy and JAX. The shared implementation sounds important enough to go into ak._v2._util as functions named something like "from_arraylib" and "to_arraylib". Passing in the module object is a good idea, too: it could be done in both, the "from" as well as the "to". If it ever becomes necessary to handle special cases for differences between NumPy, CuPy, and JAX, we can check the module.__name__ to know which one we have (without accidentally triggering an import of one of the others).

[jpivarski]

You'll probably need to merge main to get the Windows fix. But when tests pass, you can merge it!