Fix/audits

[edison0xyz]

Fixed 8 issues in audits. Exact issue is referenced in commit messages.

[zhongfu]

for #36 (floating pragma):

do we want to lock all contracts to 0.8.17, or is 0.8.15+ fine for some of them?

src/lib/EIP712.sol:pragma solidity ^0.8.15;
src/lib/MetaTxContext.sol:pragma solidity ^0.8.15;
src/lib/NativeMetaTransaction.sol:pragma solidity ^0.8.15;
src/lib/Nonces.sol:pragma solidity ^0.8.15;
test/TestSetup.sol:pragma solidity ^0.8.15;
src/FunnelFactory.sol:pragma solidity 0.8.17;
src/Funnel.sol:pragma solidity 0.8.17;
src/interfaces/IERC5827Payable.sol:pragma solidity 0.8.17;
src/interfaces/IERC5827Proxy.sol:pragma solidity 0.8.17;
src/interfaces/IERC5827.sol:pragma solidity 0.8.17;
src/interfaces/IERC5827Spender.sol:pragma solidity 0.8.17;
src/interfaces/IFunnelFactory.sol:pragma solidity 0.8.17;
src/interfaces/IFunnel.sol:pragma solidity 0.8.17;
src/mocks/MockERC1271.sol:pragma solidity 0.8.17;
src/mocks/MockSpenderReceiver.sol:pragma solidity 0.8.17;
src/mocks/TestERC20Token.sol:pragma solidity 0.8.17;
test/ERC20TestSuite.sol:pragma solidity 0.8.17;
test/ERC5827TestSuite.sol:pragma solidity 0.8.17;
test/FunnelERC20.t.sol:pragma solidity 0.8.17;
test/FunnelFactory.t.sol:pragma solidity 0.8.17;
test/Funnel.t.sol:pragma solidity 0.8.17;
test/MockSpenderReceiver.t.sol:pragma solidity 0.8.17;

---

for #45 (functions that can be declared external):

• Funnel.allowance() can probably have external visibility too -- internal functions can (and already) use _remainingAllowance() for that

---

for #44 (unclear use of virtual specifier):

there's a few functions that still have virtual specifiers that we can possibly omit:

• Funnel.computeDomainSeparator(): not much of a reason for anything in there to change in inheriting contracts (e.g. we already use name() for name)
• Funnel.permit(), Funnel.permitRenewable()
• Funnel._checkOnTransferReceived(), Funnel._checkOnApprovalReceived()
• Funnel._fallback(): though we may want to override this in inheriting contracts (e.g. to limit which functions we pass through to the base token contract???)

on the other hand:

• Funnel.supportsInterface(): may want to be able to override this in inheriting contracts, e.g. to indicate that the inheriting contract also supports other interfaces

with that said, we could probably just toss in the virtual specifier if we really do need them in the future