test: improve fungible module coverage

[skosito]

Description

Increases the coverage of mentioned parts of fungible module. Adds some generic helper methods for mocking evm client. I think there is a bit more room to move some testing code around (for example deploySystemContract) and probably it's better to mock happy paths too. Here I basically had to introduce more evm client mocking because it is hard to mimic real world evmCall reverts (and no need to in unit tests, we can mock that external dependency).

Relates to: #1742 . It is part 1 of adding more coverage, will add missing tests for system_contract.go in follow up PR.

Type of change

Tests

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Include instructions and any relevant details so others can reproduce.

• Tested CCTX in localnet
• Tested in development environment
• Go unit tests
• Go integration tests
• Tested via GitHub Actions

Checklist:

• I have added unit tests that prove my fix feature works

[lumtis]

Looks great!

[lumtis]

Great job!
The coverage looks good to me. We're integrating code coverage so will check the global coverage afterward.