chore(internal): Improve auth integration tests

[jsklan]

Description

Before, the any-auth test-definition assumed that

• request.grant_type parameter was string literal (can be enum)
• response.expires_in property was required (can be optional)

This updates the test definition to handle these cases.
Also adds any-auth to allowed-failures for typescript since this test change demonstrates that it is broken.

Changes Made

• GrantType Enum: Changed grant_type from hardcoded string literal to proper enum type with values authorization_code, refresh_token, and client_credentials across Go, Java, and Python SDKs
• Optional ExpiresIn: Made TokenResponse.expiresIn optional instead of required in all language SDKs
• TypeScript Allowed Failures: Added any-auth fixture to TypeScript SDK allowed failures list

Testing

• Updated seed test fixtures for Go, Java, and Python SDKs
• Verified all code examples and documentation reflect new type signatures
• Manual testing completed