feat: minimal rust delegate SDK

[thlorenz]

Summary

Initial minimal Rust SDK for account delegation.

Details

We don't have a Rust SDK at all at this point so here I added the minimum to make this somewhat
ergonomic to use.

With the added methods I can do the following to get the correctly initialized account metas
to include in the accounts sent to the wrapper instruction.

let (pda, _) = pda_and_bump(&player);

let delegate_accounts = DelegateAccounts::new(pda, program_id);
let delegate_metas = DelegateAccountMetas::from(delegate_accounts);
let account_metas = vec![
    AccountMeta::new(player, true),
    delegate_metas.delegate_account,
    delegate_metas.owner_program,
    delegate_metas.buffer,
    delegate_metas.delegation_record,
    delegate_metas.delegation_metadata,
    delegate_metas.delegation_program,
    delegate_metas.system_program,
];

Remaining

The PDA derivation and consts have been copied for now with a note that we need to either
move those into a core module or have the program use them via the sdk.

[GabrielePicco]

LGTM. The only comment/consideration is that tech stacks such as Rust programs with TypeScript unit tests won't use or need the added code (and vice versa; Rust clients don't need CPI and program integration utilities, and we could likely avoid some dependencies such as paste). However, the amount of code doesn't yet justify a separate crate for a Rust SDK. I’m OK with merging this now into the same crate and eventually refactoring into a separate crate if we end up adding more convenience code for Rust clients.