[C#] Unit tests

[singhk97]

Test results at #1040: https://github.com/microsoft/teams-ai/suites/18852945301/artifacts/1099928226

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1. [C#] Teams SSO auth unit tests #1053
   dotnet +1
   
2. [C#] LLMClient unit tests #1114
   dotnet +1
   
3. [C#] Sequence Augmentation unit tests #1117
   dotnet +1
   
4. [C#] OpenAIModel class unit tests #1115
   dotnet +1
   
5. [C#] Action Planner unit tests #1116
   dotnet +1
   
6. [C#] Application class unit tests #1120
   dotnet +1
   
7. [C#] TurnState unit tests #1119
   dotnet +1
   
8. [C#] Refactors, fixes and carry-overs from GA epic #907
   dotnet parity +2