Add Contract Tests for LLM Attributes and Models

[yiyuan-he]

Description of changes:
Add new contract tests for Gen AI attributes and models.

Test Plan:

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 71.54%. Comparing base (09e6487) to head (f7c0b9f).
Report is 369 commits behind head on main.

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Additional details and impacted files

@@              Coverage Diff              @@
##               main     #952       +/-   ##
=============================================
- Coverage     85.71%   71.54%   -14.17%     
- Complexity       19      305      +286     
=============================================
  Files             3       26       +23     
  Lines            49     1093     +1044     
  Branches          5      145      +140     
=============================================
+ Hits             42      782      +740     
- Misses            3      265      +262     
- Partials          4       46       +42     

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