refactor(providers): separate all email providers into individual packages

[JRocabruna]

Feature/refactor providers package

refactor(providers): separate all email providers into individual packages

Description

This pull request refactors the providers package by separating each email provider implementation into its own package. This change improves modularity and maintains a clean code structure, making it easier to manage and extend the codebase.

• Related Issue: Closes #4
• Type of Change:
  • New feature (non-breaking change which adds functionality)
  • This change requires a 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.

Additional Information

The following changes were made:

• Created individual packages for each email provider (e.g., smtp, gmail, sendgrid, etc.).
• Updated import paths in the codebase to reflect the new package structure.
• Updated documentation to match the new package structure.