support tuple instruction args

[rustopian]

Problem

Some programs, such as stake, use tuples for instruction arguments rather than structs with named fields. Codama currently does not support this pattern, and programs may not want to change their interface to use structs.

Tuple arguments are not necessarily bad practice, as the nature of these arguments can be clarified by using named types, such as stake's Initialize(Authorized, Lockup), rather than relying on struct field names for clarity.

Solution

Support tuples. Keys arg0, arg1 etc. are used for backwards compatibility.

When tuples are used in a program rather than structs with named fields, the related named type definitions should be properly decorated with #[derive(CodamaType)] so that the purpose of each argument is clear in the generated clients. The new tests briefly demonstrate how this can be done.

[lorisleiva]

Thank you for this! As discussed offline, we can add name customisation later on. Something like this:

#[derive(CodamaInstructions)]
enum FluxCapacitorInstructions {
    #[codama(account(name = "clock_sysvar"))]
    Charge(
        #[codama(name = "percentage")]
        Percentage,
        #[codama(name = "is_valid")]
        bool
    ),
}

[rustopian]

        #[codama(name = "is_valid")]
        bool

Wouldn't want to accidentally charge an invalid flux capacitor, kids.

Thanks @lorisleiva! feel free to merge whenever it's convenient 🙏