add /auth/device/code and /auth/device/poll endpoints for plugin

[warren-xu]

Overview

• Implemented steps 2 and 4 in authentication workflow.
• Added auth_connector file for backend logic of device code generation and polling as detailed in the authentication flow
• Added helpers to set device code status
• Used two Modal Dict structures to make device code lookup be O(1) time, can convert back to O(n) time if using 2 Modal Dicts is excessive. This will be needed for the /auth/device/authorize endpoint (which I did not implement because firebase admin sdk was not set up)

[eshaan-mehta]

Should make another pr for adding tests. Otherwise looks good!