fix: update codebase to Awkward 2.0.0.

[jpivarski]

I wasn't able to test locally. I think I got all the right changes. Let's see what CI thinks.

[jpivarski]

Oh wait—I have to remove debugging code.

[jpivarski]

I guess I read the pytest output from Round 1 incorrectly: there was one error causing three test failures. With that error fixed, the other two didn't need to be debugged.

So it's done!

To explain the changes, most of them are just renaming, but in some of them, I replaced a lot of

isinstance(layout, (ak.layouts.ThisArray, ak.layouts.ThatArray))

with

layout.is_this or layout.is_that

These "is_*" booleans are categories of similar array types. All of the integer-sized type variations are gone (e.g. ListArray64 versus ListArray32), which would have simplified the isinstance calls on its own, but these "is_*" also identify commonly selected groups (e.g. is_list is True for ListArray, ListOffsetArray, and RegularArray).

I removed code that depends on now-nonexistent types, PartitionedArray and VirtualArray. For the tests, however, I just changed the PartitionedArray test to work on a concatenated array and the VirtualArray test to work on eager data.

I also introduced use of the copy method to change one field of a layout node, rather than rebuilding the whole layout node. (If I hadn't done that, I would also have needed to remove references to the identities, which have been removed.)

I scanned over the changes once again, and yeah: it was mostly renaming.

[jmduarte]

LGTM!