Add type hints to parsers

[GlassOfWhiskey]

This commit enables type hints within Python generated parsers. by refactoring how the codegen logic handles instance types. Results are fully-typed Python objects ready to be compiled with mypyc.

[codecov]

Codecov Report

❌ Patch coverage is 98.52941% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 83.32%. Comparing base (734fbc0) to head (67cd201).

Files with missing lines	Patch %	Lines
schema_salad/python_codegen.py	98.50%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #993      +/-   ##
==========================================
+ Coverage   83.23%   83.32%   +0.08%     
==========================================
  Files          22       22              
  Lines        5023     5042      +19     
  Branches     1195     1199       +4     
==========================================
+ Hits         4181     4201      +20     
+ Misses        559      558       -1     
  Partials      283      283              

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