move and rename eltype conversion

[TendonFFF]

Checklist

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Description

Move _change_eltype in CUDA extension to utilities.jl and rename it as _convert_eltype_wordsize

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.39%. Comparing base (e76fcbe) to head (a028c37).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #430   +/-   ##
=======================================
  Coverage   94.39%   94.39%           
=======================================
  Files          47       47           
  Lines        2998     2998           
=======================================
  Hits         2830     2830           
  Misses        168      168           

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