Fix card due date

[zsh-eng]

Currently, we update the due date of the card locally by changing the .due field on the Card.

This is the wrong way of updating cards as it means other details, such as stability, State, etc. are not being updated.
Instead, we should abstract out the functionality of updating the card using the ts-fsrs library and reuse these functions on both the frontend and the backend to ensure that updates are in sync.