[DevEx]: Refactor test selectors to use helpers and card ids

[itsalaidbacklife]

Improvement Summary

We should refactor the way that tests select GameCard elements in the DOM to use helper functions and the ids of cards, rather then rank-suit strings

Detailed Description

Currently all the cypress tests identify cards in the DOM via a selector pattern of data-{location}-card={rank-suit} e.g. data-player-hand-card=0-13 for the king of clubs in the player's hand. We can simplify this in two ways:

• Update these selectors in the DOM to use the cards' ids rather than rank-suit strings e.g. `data-player-hand-card=KC for the king of clubs in the player's hand
• Define an enum with all the values for where cards can be e.g. CardLocation.PLAYER_HAND, CardLocation.OPPONENT_POINTS with string values for all the different selector locations
• Create a function getCard(card, location) which inputs a card object and location (string enum) that calls cy.get() to get the chosen card in the chosen location
• e.g. this would call cy.get(data-${location}-card="${card.id}" to get the selected card and allow chaining
• Update all the existing test code selecting cards to call the above helper.
• Update the docs to describe this new pattern

This will offer a more transparent selector pattern for test code that supports better autocompletion