test: add empty test files so packages are included in coverage

[skosito]

Description

Add empty test files in packages without any tests so they are included in coverage with 0%, instead of completely ignored.
This is added only for packages that are supposed to be included (cross checked with ignored files in codecov).

Check issue for more information on why is this needed.

For reference, codecov report for this branch: https://app.codecov.io/gh/zeta-chain/node/tree/test-add-missing-test-files/zetaclient
vs codecov report for develop branch: https://app.codecov.io/gh/zeta-chain/node/tree/develop/
(check packages where empty test files are added in this PR, they are ignored on develop codecov)

Closes: #1893

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

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 48.55%. Comparing base (a824f4e) to head (c09ee5e).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1899      +/-   ##
===========================================
- Coverage    49.95%   48.55%   -1.40%     
===========================================
  Files          220      232      +12     
  Lines        12722    13098     +376     
===========================================
+ Hits          6355     6360       +5     
- Misses        5925     6296     +371     
  Partials       442      442              

see 12 files with indirect coverage changes