feat: improve and fix delayed length calculations and add delayed length calculation for layouts that need it

[ikrommyd]

Partial fix for #3888
Tackles Bug 1 only

[ikrommyd]

This is actually funny. It's always been testing the wrong thing given the error message it wants to raise

[github-actions]

The documentation preview is ready to be viewed at http://preview.awkward-array.org.s3-website.us-east-1.amazonaws.com/PR3889

[codecov]

Codecov Report

❌ Patch coverage is 85.00000% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 82.66%. Comparing base (a6c3b25) to head (060c3d2).

Files with missing lines	Patch %	Lines
src/awkward/contents/bitmaskedarray.py	75.00%	2 Missing ⚠️
src/awkward/operations/ak_from_buffers.py	83.33%	2 Missing ⚠️
src/awkward/contents/recordarray.py	88.88%	1 Missing ⚠️
src/awkward/contents/regulararray.py	90.90%	1 Missing ⚠️

Additional details and impacted files

Files with missing lines	Coverage Δ
src/awkward/contents/bytemaskedarray.py	88.40% <ø> (ø)
src/awkward/contents/unionarray.py	86.56% <ø> (ø)
src/awkward/contents/recordarray.py	85.58% <88.88%> (+0.45%)	⬆️
src/awkward/contents/regulararray.py	87.19% <90.90%> (+0.15%)	⬆️
src/awkward/contents/bitmaskedarray.py	70.14% <75.00%> (+0.11%)	⬆️
src/awkward/operations/ak_from_buffers.py	92.73% <83.33%> (-0.66%)	⬇️

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[ianna]

content.length usually measures bytes, while the length variable might represent the expected size in bits.

[ikrommyd]

This is the whole snippet (without my changes)

        if (
            content.backend.nplike.known_data
            and length is not unknown_length
            and mask.length is not unknown_length
            and length > content.length * 8 
        ):
            raise ValueError(
                f"{type(self).__name__} 'length' ({length}) must be <= len(content) ({content.length})"
            )

So I think this was meant to check whether length > content.length. The length of the mask is checked right above for length > mask.length * 8. Only mask.length is in bits as far as I know/can understand. .length is always the "physical" length of the layout/array. So length and content.length are neither in bytes nor bits in general. It's the "number of elements" (which does correspond to bytes of the mask in this case).