Cleanup implementation of goto binary reading

[thomasspriggs]

This refactoring PR is preparatory work for #7633

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• Methods or procedures I have added are documented, following the guidelines provided in CODING_STANDARD.md.
• The feature or user visible behaviour I have added or modified has been documented in the User Guide in doc/cprover-manual/
• Regression or unit tests are included, or existing tests cover the modified code (in this case I have detailed which ones those are in the commit message).
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[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.14 🎉

Comparison is base (417d362) 78.36% compared to head (53bb8fd) 78.51%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #7635      +/-   ##
===========================================
+ Coverage    78.36%   78.51%   +0.14%     
===========================================
  Files         1671     1671              
  Lines       191829   191845      +16     
===========================================
+ Hits        150328   150620     +292     
+ Misses       41501    41225     -276     

Impacted Files	Coverage Δ
src/goto-programs/read_bin_goto_object.cpp	90.22% <100.00%> (+1.33%)	⬆️

... and 16 files with indirect coverage changes

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