feat/add full ts support/coverage

[PatrykKuniczak]

* Please fill in the required items.

Priority*

• [x] High: This PR needs to be merged first for other tasks.
• [ ] Middle: This PR should be merged quickly to prevent conflicts due to common changes. (default)
• [ ] Low: This PR does not affect other tasks, so it can be merged later.

Purpose of the PR*

As we was talking on Discord, i've decided to refactor project a little and create it more ts friendly. It'll be also very helpful for me, when i'll be working on custom env module, because i've some conflicts, now it should works perfect :)

Don't pay attention to redundant cross-env and overall env solutions because it'll be refactored #722 I'm currently working on this/

Changes*

I've changed .js to .ts where it's necessary

How to check the feature

Run it as normal pnpm build or/and pnpm dev And check if all pages works well on Chrome and Firefox :)

[PatrykKuniczak]

CI build error will dissapear after #748 let's merge it in the first place