Simple OFT Airdrop

Simple OFT Airdrop contracts, inspired by Arbitrum's ARB token airdrop and powered by LayerZero.

Potential considerations, modifications and variations to the SimpleAirdrop.sol contract:

• Make the claim process non-pausable by removing the use of Pausable.sol from the contract.
• Make the leftover tokens be burned instead of being sent to the owner.
• Enforce airdrop start and end dates.
• Don't allow the owner to sweep or burn the leftover tokens before the airdrop end date.
• Introduce multiple airdrop rounds.
• Include token transfers directly into the setRecipients function. (note that this approach will consume significantly more gas)