Refactor structure and union initializer generators

[MrYoranimo]

Fixes #130.

The upcoming release of Python 3.14 brings a breaking change in the way (the order of) constants used in a function is/are determined while compiling bytecode. In previous versions of Python, the first co_consts entry was both used to determine the presence of a docstring for a function (None if absent) and to provide the docstring. However, since the presence indicator has been replaced with a flag in the co_flags bitfield, None is not necessarily the first co_consts entry anymore in case no docstring was present.

While this change would only affect generated union initializers, this PR refactors the generators for both the structure and the union initializers to overwrite tuples in the initializer function's code object based on their name instead of trying to recreate the tuples based on a static order, in an attempt to stabilize the generators against future regressions.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.73%. Comparing base (a7ec0a3) to head (aef481a).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #136      +/-   ##
==========================================
+ Coverage   92.21%   92.73%   +0.52%     
==========================================
  Files          21       21              
  Lines        2517     2381     -136     
==========================================
- Hits         2321     2208     -113     
+ Misses        196      173      -23     

Flag	Coverage Δ
unittests	92.73% <100.00%> (+0.52%)	⬆️

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[Schamper]

Made some slight changes to deal with non-hashable type lookups (in case they sneak in somewhere) and let Copilot generate some docstrings.