add method to extract values from modals

[laralove143]

while it's rather simple it ends up being a bit of boilerplate when extracting multiple components' values, im not sure if theres a need for this for other components, since always have a single value

it should be a trait on ModalInteractionData that simply takes a custom_id and returns an option, this has the limitation of returning a reference so that it doesnt consume it (since it probably has more components)

the trickier bit is consuming the data and returning a [String] so that it can be destructed, it could be collected to a HashMap or struct but former is overhead and latter requires proc macros and for the user to create a struct

this can be done using const generics

fn values<const N: usize>(self, custom_ids: [&str; N]) -> [String; N];

although this requires that the users provide the custom_ids statically, it can be used like

let [val1, val2] = data.values(["val1", "val2"])?; // returns error if not enough values