zkvm: return () instead of &mut Program from the closure in Program::build

[oleganza]

Here's a real use with an awkward ending line:

let program = zkvm::Program::build(|p| {
    for stored_utxo in spent_utxos.iter() {
        p.push(stored_utxo.contract());
        p.input();
        p.sign_tx();
    }

    let pmnt = payment_receiver.blinded_value();
    p.push(pmnt.qty);
    p.push(pmnt.flv);

    p.cloak(
        spent_utxos.len(),
        maybe_change_receiver_witness.as_ref().map(|_| 2).unwrap_or(1),
    );

    p.push(payment_receiver.predicate());
    p.output(1);

    // TBD: change the API to not require return of the `&mut program` from the closure.
    p
});

[dltmd6262]

Hi, this looks like something I can take up. I'm interested in tackling more issues here, can you decide if this would be a good starting issue for me?

[oleganza]

Sure, this should be a good starting point. Please don’t forget about crates token, account and demo that use this API - would be good to update them in one PR. Thank you!

[dltmd6262]

Great! I'll make sure the tests and builds pass in those crates too.