feat: support scalars in TypeTracer operations

[agoose77]

Fixes #1703

This PR:

• adds support for JAX arrays in ak.Array
• adds support for TypeTracerArray in ak.to_layout
• tightens isinstance to ak._util.is_sized_iterable in ak.fill_none
• removes iterator support from TypeTracerArray.from_array and refactors its usage

[codecov]

Codecov Report

Merging #1774 (9ffc432) into main (df377bd) will increase coverage by 0.01%.
The diff coverage is 72.72%.

Additional details and impacted files

Impacted Files	Coverage Δ
src/awkward/contents/numpyarray.py	90.05% <ø> (ø)
src/awkward/operations/ak_fill_none.py	89.74% <ø> (-0.26%)	⬇️
src/awkward/operations/ak_to_layout.py	80.39% <62.50%> (+1.32%)	⬆️
src/awkward/highlevel.py	75.70% <75.00%> (-0.09%)	⬇️
src/awkward/_typetracer.py	74.90% <84.61%> (+0.37%)	⬆️
src/awkward/contents/indexedarray.py	79.76% <0.00%> (-0.19%)	⬇️
src/awkward/contents/recordarray.py	83.72% <0.00%> (-0.18%)	⬇️
src/awkward/_util.py	81.95% <0.00%> (-0.18%)	⬇️
src/awkward/_connect/avro.py	87.17% <0.00%> (-0.14%)	⬇️
src/awkward/types/_awkward_datashape_parser.py	47.72% <0.00%> (-0.01%)	⬇️
... and 2 more

[jpivarski]

The is_own_array thing is showing its usefulness and generality here.

Everything looks good to me!