refactor: allow non-void get_or_make_function

[ss2165]

No description provided.

[codecov]

Codecov Report

❌ Patch coverage is 67.39130% with 15 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (feat/barray-llvm@2d1c8c3). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
...ugr-llvm/src/extension/collections/borrow_array.rs	64.28%	8 Missing and 2 partials ⚠️
hugr-llvm/src/emit/func.rs	72.22%	2 Missing and 3 partials ⚠️

Additional details and impacted files

@@                 Coverage Diff                 @@
##             feat/barray-llvm    #2609   +/-   ##
===================================================
  Coverage                    ?   83.19%           
===================================================
  Files                       ?      255           
  Lines                       ?    50009           
  Branches                    ?    45520           
===================================================
  Hits                        ?    41603           
  Misses                      ?     6049           
  Partials                    ?     2357           

Flag	Coverage Δ
python	91.42% <ø> (?)
rust	82.37% <67.39%> (?)

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