OFT v2 Refactoring to support uint256 amount

[0xIryna]

The scope of this PR:

1. Remove type(uint64).max limit for amount from OFTV2Core, ProxyOFTV2 and ProxyOFTWithFee
2. Introduce OFTV2Aptos, ProxyOFTV2Aptos, ProxyOFTWithFeeAptos that allow no more than 6 shared decimals and have type(uint64).max limit for amount
3. Replace abi.encodePacked with abi.encode in OFTV2Core and derived contracts
   Using abi.encodePacked makes encoding inconsistent with previous versions and decoding ugly. Additionally, abi.encodePacked will be removed in a future version of Solidity (see Remove abi.encodePacked ethereum/solidity#11593)

NOTE: there isn't a good way to extract all Aptos overrides in one contract (diamond inheritance problem), thus the same code is duplicated in OFTV2Aptos, ProxyOFTV2Aptos, and ProxyOFTWithFeeAptos contracts. The same issue is present in ProxyOFTV2 and ProxyOFTWithFee