feat: move operations to nested Auth and User structs

[ctran88]

What's New?

• moves auth operations under a nested Auth struct
• moves user operations under a nested User struct
• keeps the set_server_url func to maintain tests until they are moved to the e2e suite
• removes the get_app func since it doesn't really serve much purpose except for a test of the sdk without inducing any side effects

Screenshots (if appropriate):

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have manually tested my code thoroughly
• I have added/updated inline documentation for public facing interfaces if relevant
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing integration and unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

Additional context