Docs/update package documentation

[JRocabruna]

Description

This pull request includes updates to improve the documentation and organization of the gomail project. The changes include:

• Updated gomail.go documentation: Improved clarity on pkg.go.dev by wrapping the common package functions.

• Added tests: Ensured test coverage for the wrapped functions to maintain the integrity of the project.

• Added common/doc.go: Provided package-level documentation for the common package, detailing its utilities and usage.

• Type of Change:

  • Documentation update

Checklist

Please ensure the following guidelines are met:

• [x] The code follows the style guidelines of this project.
• [x] A self-review has been performed on the code.
• [x] The code is well-documented, and comments have been added where necessary.
• [x] Tests have been added to prove that the fix is effective or that the feature works. All existing tests pass.
• [x] Commit messages follow the convention type(scope): description.
• [x] The pull request has no conflicts with the base branch.
• [x] Any dependent changes have been merged and published in downstream modules.