feat: Add Unit Tests

[marverix]

Hi,

I had a bit of trouble debugging the code, because no functions were not exported, nor there were Unit Tests. So I split the code to smaller parts, which now helps people willing to contribute better understand what's going on etc. This also enabled me to write some basic unit tests using jest.

I have also introduced a new workflow, which is triggered on each commit to every branch (so now one can work on branch and run unit tests). Using workflow_call I also added it so that it precedes the deploy job.

In the end there were no bugs in your code whatsoever, but mine misunderstanging of how BREAKING CHANGE works in CC :)

Last, but not least, thank you for this GitHub Action!