refactor: removed unused code and unified tx signing logic

[ws4charlie]

Description

The PR is a minimum refactor to prepare for EIP-1559 outbound transaction

• removed unused method SignWhitelistTx
• unified different tx signing (onReceive, on Revert, erc20 withdraw, gas token withdraw) to use a common method Sign.
• unified the tx verification logic in unit tests; added missing unit tests for SignCancelTx and TestSigner_SignMigrateTssFundsCmd
• fix 'amount' issue in SignMigrateTssFundsCmd

Closes:

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

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

[codecov]

Codecov Report

Attention: Patch coverage is 89.74359% with 4 lines in your changes missing coverage. Please review.

Project coverage is 69.68%. Comparing base (26b4f69) to head (7493354).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2306      +/-   ##
===========================================
+ Coverage    69.44%   69.68%   +0.23%     
===========================================
  Files          281      281              
  Lines        16654    16644      -10     
===========================================
+ Hits         11565    11598      +33     
+ Misses        4604     4570      -34     
+ Partials       485      476       -9     

Files	Coverage Δ
zetaclient/chains/evm/signer/signer.go	53.97% <89.74%> (+7.66%)	⬆️

[lumtis]

This looks legit to me. Some few comments.

Wondering if we could think about a further refactoring with a declarative approach?
We have a single sign function and an array containing the different values depending on the tx to sign.
Then to support a new tx that can be signed, you only need to add an entry in this array

[ws4charlie]

This looks legit to me. Some few comments.

Wondering if we could think about a further refactoring with a declarative approach? We have a single sign function and an array containing the different values depending on the tx to sign. Then to support a new tx that can be signed, you only need to add an entry in this array

I think we can create a issue to track this: #2318