Feature instant swap

[marco-sundsk]

• Instant swap
  • users can swap directly using ft_transfer_call without deposit and withdraw;
  • old users's inner ref assets won't be touched in successful situation;
  • Any failure before swap completion would cause a refund of token_in token back to user's wallet;
  • Any failure after swap completion would cause token_out token into inner account or lost-found account;

[marco-sundsk]

Considering internal_send_tokens takes around 50Tgas, we can only do around 5 token transfers, but that's probably fine, since instant swap right now should lead to sending only one token.

Failure is permitted, but token loss isn't. So I think we need ensure even in that situation (gas insurfficent to send all tokens), the whole instant-swap would fail before cross-contract calls, to make the ft_transfer_call failure without any token transferred to ref.