Patch Release: Refactor OAuth models to structs, extend OAuthUser, and update Vapor

This pull request introduces several improvements to the OAuth implementation:

Key Changes:

Refactored OAuth models to use structs: Enhanced model efficiency and value semantics by transitioning OAuth models from classes to structs.
Extended OAuthUser struct: Expanded OAuthUser struct functionality to accommodate additional capabilities.
Refactored OAuthClient and OAuthResourceServer models: Optimized model structure for improved performance and maintainability.
Upgraded Vapor package to version 4.91.1: Ensured compatibility with the latest Vapor features and bug fixes.

Benefits:

Improved performance and memory usage: Struct-based models offer potential performance gains and more efficient memory management.
Enhanced code readability and maintainability: The refactored code adheres to best practices and promotes better understanding.
Access to latest Vapor features: The updated Vapor package provides access to bug fixes, enhancements, and potential new functionalities.

vamsii777 / vapor-oauth