ERC20Custody.sol has a divergence in the implementation regarding fees, consider the following:
The deposit function along with the constructor are causing this divergence, as constructor allow zeta to be address(0) at construction, which deposit account for in the following code, but then if zetaFee are modified later on (Zeta wants to start charging fees on ERC20 deposits), those fees will never be able to be charged in case zeta was passed as address(0) at constrution.
So I would recommend the following changes to mitigate this. While we are here, I would also suggest to add a validation for zetaMaxFee in the constructor since its immutable too.
https://github.com/code-423n4/2023-11-zetachain/blob/main/repos/protocol-contracts/contracts/evm/ERC20Custody.sol#L177
