Adding an alloc_array function

[aadit-n3rdy]

This PR solves #440 and adds an alloc_array function. All uses of alloc_mem which can be replaced with alloc_array have been replaced with alloc_array. A test for stumpless_copy_entry has been added as well.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.54%. Comparing base (1bd3333) to head (d8c8e05).
Report is 1 commits behind head on latest.

Additional details and impacted files

@@            Coverage Diff             @@
##           latest     #458      +/-   ##
==========================================
+ Coverage   90.35%   90.54%   +0.19%     
==========================================
  Files          47       47              
  Lines        4374     4379       +5     
  Branches      586      587       +1     
==========================================
+ Hits         3952     3965      +13     
+ Misses        287      280       -7     
+ Partials      135      134       -1     

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[aadit-n3rdy]

Both the failed tests were in calls to alloc_mem, is this a problem with alloc_array? I'll look into this as well.

EDIT: Scratch that, forgot to free the entry I created in the test. My bad.

[goatshriek]

Excellent work! Just a few cleanup items: make sure that you aren't using tabs anywhere, and move the large struct into the new test instead of making it a fixture structure.