Modal derive macros

[gpluscb]

Adds two derive macros ModalModel and CreateModal as analogues to CommandModel and CreateCommand.

Short example:

#[derive(CreateModal, ModalModel)]
#[modal(
    title = "Give me your credit card information.",
    custom_id = "modal_demo::ExampleModal"
)]
pub struct ExampleModal {
    #[modal(label = "Credit card information here", style = "short")]
    credit_card_information: String,
}

let custom_id = interaction.id.to_string();
let response = ExampleModal::create_modal(custom_id.clone()).into();
interaction_client.create_response(interaction.id, &interaction.token, response).await?;

magic_event_provider.on_event(|event| async {
    let Event::InteractionCreate(interaction) = event else {
        return;
    };
    
    let interaction = interaction.0;
    if InteractionType::ModalSubmit != interaction.kind {
        return;
    }
    
    let Some(InteractionData::ModalSubmit(modal_data)) = interaction.data else {
        return;
    };
    
    if custom_id != modal_data.custom_id {
        return;
    }
    
    let modal = match ExampleModal::from_interaction(modal_data.into()).expect("couldn't parse modal");
    
    println!("Got someone's credit card info, it's {}!", modal.credit_card_information);
})

Draft pending

• Some TODOs in the code
• Documentation
• A rework of the custom_id handling to allow generating it at runtime
• Some more consideration whether the error types used are any good for this use-case
• New changes to modals https://discord.com/developers/docs/change-log#introducing-new-modal-components

Regarding the custom_id handling:
A custom_id needs to be able to be set at runtime, otherwise it is impossible to distinguish replies for different instances of the same modal from each other.
To solve this, I plan to remove the custom_id attribute and instead give the create_modal function a custom_id parameter.
This has been solved by removing the custom_id attribute and instead giving the create_modal function a custom_id parameter.

Closes #15

[gpluscb]

I also am not sure if main is the correct target branch, so feel free to change that

[gpluscb]

PR will need a rework for the new modal changes (https://discord.com/developers/docs/change-log#introducing-new-modal-components)