fix: some usages of len(layout) under typetracer

[agoose77]

This PR fixes a few (but certainly not all) places where we're using len(layout), or otherwise relying on a layout to be non-typetracer

[agoose77]

@lgray this would fix dak.with_name() without the meta bypass.

[codecov]

Codecov Report

Merging #2181 (163b1d3) into main (a91d96b) will increase coverage by 0.04%.
The diff coverage is n/a.

Additional details and impacted files

Impacted Files	Coverage Δ
src/awkward/operations/ak_full_like.py	98.18% <ø> (ø)
src/awkward/operations/ak_with_name.py	100.00% <ø> (ø)
src/awkward/contents/recordarray.py	84.91% <0.00%> (+0.41%)	⬆️
src/awkward/index.py	90.44% <0.00%> (+0.63%)	⬆️
src/awkward/_nplikes/typetracer.py	74.02% <0.00%> (+0.74%)	⬆️
src/awkward/_errors.py	80.52% <0.00%> (+1.05%)	⬆️

[lgray]

Can this one be merged to main or waiting for something?

[jpivarski]

It was waiting for my review.

It's all good! Replacing len(layout) with layout.length is something we should be doing everywhere, ever since the length property was introduced (since it does not require the result to be an integer).