fix: remove index_nplike

[pfackeldey]

Awkward does not support index_nplike anymore with scikit-hep/awkward#3446 (we need to wait for a new release here). This PR replaces index_nplike with nplike.

[codecov-commenter]

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.10%. Comparing base (8cb8994) to head (8263b62).
Report is 252 commits behind head on main.

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #579      +/-   ##
==========================================
- Coverage   93.06%   92.10%   -0.97%     
==========================================
  Files          23       24       +1     
  Lines        3290     3596     +306     
==========================================
+ Hits         3062     3312     +250     
- Misses        228      284      +56     

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[martindurant]

This looks complete - any reason to keep it as draft?

[pfackeldey]

I wanted to wait for the corresponding awkward release and pin the version. Not sure when we get it'll be released though.

[martindurant]

Isn't it the case that index_nplike went away, but nplike was already there - so it doesn't need the latest awkward at all? Or maybe I misunderstood.

[pfackeldey]

Oh you're completely right! Somehow I haven't thought about this being backwards compatible, but it is 😅

[martindurant]

OK, now let's do #578