Improve Multi ASA contract and trim down total compiled size

[aorumbayev]

The goal is to follow up and address comments mentioned in the following PR -> AlgoWorldNFT/algoworld-swapper#18

Swapper contract can fit up to 5 ASAs with PR 18 merged, but can be trimmed down even further and total ASAs per swap can increase to a higher value (~6-10 ASAs).