Change Draft data structure

[loothero]

The current data structure for Draft is inefficient because each time we pick a card, we re-write all the previous rounds of draft data to storage. Furthermore, the use of Span<> prevents us from leveraging IntrospectPacking such that every u8 option and u8 card is consuming an entire storage slot.

By using a hashmap, we can prevent rewriting previous data each time a new card is selected. Furthermore, by storing the seed which can be used to produce the card options instead of the actual card ids, we can eliminate the other span and pack Draft into a single storage slot

#[derive(Copy, Drop, Serde, IntrospectPacked)]
#[dojo::model]
pub struct Draft {
    #[key]
    game_id: u64,
    #[key]
    draft_round: u8,
    selected_card: u8
    seed: u128
}

With a simple helper function, we can still generate a Span<u8> of the cards or options when needed but the storage, and therefore gas, of the above data structure will be significantly more efficient.  

[Await-0x]

For this to work, we also need to store the current draft_count somewhere