[C#] feat: add unit tests for Teams SSO auth related classes

[blackchoey]

Linked issues

closes: #1053 #1110

Details

1. Create an adapter for MSAL library to make the classes testable with mock
2. Update existing class implementation to use the MSAL library adapter
3. Do not check token cache in TeamsSsoPrompt because the Authentication handler already checks token cache before invoking the prompt
4. Add unit tests

Attestation Checklist

• My code follows the style guidelines of this project

• I have checked for/fixed spelling, linting, and other errors

• I have commented my code for clarity

• I have made corresponding changes to the documentation (we use TypeDoc to document our code)

• My changes generate no new warnings

• I have added tests that validates my changes, and provides sufficient test coverage. I have tested with:

  • Local testing
  • E2E testing in Teams

• New and existing unit tests pass locally with my changes