plan_kernel
Return the array function this call is, or None to touch no data.
Both metadata objects are given because a kernel often needs the difference between them – transpose wants the permutation which takes the old dimension order to the new.
The default finds a kernel registered for the data’s backend, and failing that the class’s own kernel, which is written to the array API standard and so runs on any of them. A class with no kernel at all is a metadata-only operation and gets None.