feat: allow multiple declarations of the same property in discriminat…

[shannenigans]

Issue #, if available:

Description of changes:
Picks the first non-never property when multiple declarations are provided

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.57%. Comparing base (b2851ce) to head (3ff74c8).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #120      +/-   ##
==========================================
- Coverage   95.11%   94.57%   -0.55%     
==========================================
  Files          11       11              
  Lines         512      516       +4     
  Branches      139      142       +3     
==========================================
+ Hits          487      488       +1     
- Misses         25       28       +3     

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[ernst-dev]

Could you add more tests to meet the codecov requirements?