fix: EmptyArray.is_numpy should be False.

[jpivarski]

EmptyArray.is_numpy is now False because it's surprising. (EmptyArrays are sometimes coerced to being NumpyArrays with dtype=np.float64 to match the NumPy behavior, but in general, EmptyArray represents an unknown type, not a NumPy-like type.)

There's already EmptyArray.is_unknown to identify them, and everywhere that we actually cared about it, we were already checking for it:

% fgrep -r '.is_numpy' --include \*.py src/awkward
src/awkward/contents/listarray.py:            if not content.is_numpy or not content.parameter("__array__") == "char":
src/awkward/contents/listarray.py:            if not content.is_numpy or not content.parameter("__array__") == "byte":
src/awkward/contents/listoffsetarray.py:            if not content.is_numpy or not content.parameter("__array__") == "char":
src/awkward/contents/listoffsetarray.py:            if not content.is_numpy or not content.parameter("__array__") == "byte":
src/awkward/contents/regulararray.py:            if not content.is_numpy or not content.parameter("__array__") == "char":
src/awkward/contents/regulararray.py:            if not content.is_numpy or not content.parameter("__array__") == "byte":
src/awkward/operations/ak_unflatten.py:        elif counts.is_numpy or counts.is_unknown:
src/awkward/operations/ak_is_none.py:        elif layout.is_numpy or layout.is_unknown or layout.is_list or layout.is_record:
src/awkward/operations/ak_transform.py:        ...     if layout.is_numpy:
src/awkward/operations/ak_transform.py:        ...     if layouts[0].is_numpy and layouts[1].is_numpy:

The first section really wants only NumpyArray because it's checking for arrays of char or byte, which EmptyArray is not. The last two, in ak_transform.py, are examples in docstrings. Everything else already checks for is_numpy or is_unknown.

Demonstrably, it does not affect any tests.

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📚 The documentation for this PR will be available at https://awkward-array.readthedocs.io/en/jpivarski-emptyarray.is_numpy-should-be-false/ once Read the Docs has finished building 🔨

[codecov]

Codecov Report

Merging #1971 (b05cf7a) into main (e5836e9) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

Additional details and impacted files

Impacted Files	Coverage Δ
src/awkward/contents/emptyarray.py	72.43% <ø> (-0.15%)	⬇️
src/awkward/operations/ak_is_none.py	96.55% <100.00%> (ø)