fix: make to_packed work for typetracer backed IndexedOptionArray, BitMaskedArray, and UnionArray

[ikrommyd]

Fixes #3607

This PR also adds testing for to_packed for all layouts with typetracer backend which wasn't tested so far.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.67%. Comparing base (b749e49) to head (3cd7f3b).
⚠️ Report is 417 commits behind head on main.

Additional details and impacted files

Files with missing lines	Coverage Δ
src/awkward/contents/bitmaskedarray.py	70.02% <100.00%> (-0.41%)	⬇️
src/awkward/contents/bytemaskedarray.py	87.64% <100.00%> (-2.02%)	⬇️
src/awkward/contents/indexedoptionarray.py	89.09% <100.00%> (+0.87%)	⬆️
src/awkward/contents/unionarray.py	86.33% <100.00%> (+1.08%)	⬆️

... and 193 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[ikrommyd]

@agoose77 could you please take a quick look at my UnionArray changes because to_packed there had zero typetracer handling. I don't know if the If X is not unknown_length statements I added there are correct or if I'm missing something and it requires some extra checks in the typetracer case. What's certain is we definitely can't do data dependent decisions with typetracers but I don't know if it needs extra handling there.

[pfackeldey]

Thanks! This does look good to me 👍

This PR is ready from my side :)

Let's see if @agoose77 has some comments before we merge, ok?

[github-actions]

The documentation preview is ready to be viewed at http://preview.awkward-array.org.s3-website.us-east-1.amazonaws.com/PR3608

[ianna]

@ikrommyd - I still see some unresolved comments. Do you think we could on the comments agree soon-ish? Thanks.

[ianna]

@ikrommyd - thanks for addressing the comments! I'm merging it for the upcoming release.