Fix verify_transfer_with_fee_proof broken by Rust 1.79.0

[LucasSte]

Problem

Rust does not have a stable ABI, so Rust programs are subject to changes in their memory layout. Rust 1.79.0 will break function verify_transfer_with_fee_proof with the following error:

Error: Function _ZN14spl_token_20229extension21confidential_transfer12verify_proof30verify_transfer_with_fee_proof17h830056199538c531E Stack offset of 4512 exceeded max offset of 4096 by 416 bytes, please minimize large stack variables. Estimated function frame size: 4576 bytes.

This will make the following tests fail:

    confidential_transfer_transfer_with_fee_and_split_proof_context
    confidential_transfer_transfer_with_fee_and_split_proof_context_in_parallel

Solution

I split the function in two new methods.

[samkim-crypto]

@LucasSte, this function is actually on the way out with some of the new upcoming refactoring changes in the SPL repo. Can you give me a couple days to have these changes put in first?

[LucasSte]

@LucasSte, this function is actually on the way out with some of the new upcoming refactoring changes in the SPL repo. Can you give me a couple days to have these changes put in first?

Yes, no problem. Let me know when you are ready.

[joncinque]

@LucasSte, I think @samkim-crypto has finished his work here -- do the tests pass if you use SPL's current master?

[LucasSte]

All tests are passing now. Thanks!