refactor: ERC-20 deposit

[brunomenezes]

Summary

Some refactoring was done to the logic handling the erc-20 deposit, previously done by a public method called handlePayload(). After adding code for erc-721 deposits, the idea is to have the same method naming to deal with its own piece of logic. Also, method visibility was applied, so each prepare*() is private, so tests should only be done through the handle() method and then expectations are checked.

Changelog:

• Move erc-20 deposit logic handling to the prepareErc20Deposit(), including its storage setting and related logging.
• Remove the handlePayload() method.
• Set params for both prepare*() methods as a const tuple and use spread to pass down to each method.
• Set both prepare* method visibility to private.
• Remove tests that were targeting implementation details in the past, i.e. handlePayload().
• Also applied a bit of refactoring in the testing setups and mockings in general.

[brunomenezes]

That is odd. The Overall Coverage dropped. That is for the OwnershipTransferred, let me check a case.