Upgrade solidity pragma to ^0.8.13

[ZzzzHui]

@guidanoli proposed to use a type-safe way to encode function calls (see here), which is already adopted in branch feature/blockchain-agnostic-inputs.
Since this new feature abi.encodeCall was introduced in 0.8.11 and bug fixed in 0.8.13 (ref), we'll upgrade solidity to pragma solidity ^0.8.13;

[guidanoli]

You can upgrade the pragma of all contracts, since they are all connected to contracts that will need to be redeployed for v2 anyway. :-)

[guidanoli]

Actually, now v2 will not trigger a redeployment of all contracts.
Therefore, let's only fix this by the end of v2, only for the contracts that were changed.