Adopt DRY principle and enhance performance

[felipeplets]

I've refactored multiple-files.converter.ts and single-file.converter.ts to enhance DRY principle in the project.
To read more about DRY: https://en.wikipedia.org/wiki/Don%27t_repeat_yourself

I've also introduced a major performance improvement by processing files in parallel using Promise.all instead of a linear approach.

I've performed a couple of tests with the old and new code and they are currently producing the same result. I recommend raising the Unit Tests coverage in order to enable project growth.

[kreuzerk]

🤩Epic! Thx a lot.

One thing, our build is configured to release automatically based on conventional commits. So usually our commit messages follow the conventional commits standard. https://www.conventionalcommits.org/en/v1.0.0/

Another thing, you are doing awesome work here, therefore I added you as a collaborator to the project. This means you can now create PR's directly on this project and don't need to fork.

[felipeplets]

Thank you for the feedback, I did not know the Conventional Commits standards before, I will learn about it for my next commits.

Thanks for adding me as contributor, much appreciated.

[kreuzerk]

🎉 This PR is included in version 4.2.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀