feat: move to using postcss-js-core

[43081j]

Work in progress of the extraction of the core.

It works, tests pass, i just need to move all the tests around a bit and actually publish the repo/package.

then ill probably do a PoC of some other syntax to make sure it covers the right use cases, before merging

Fixes #41

[43081j]

minor update - just getting all the tests written for the new core, then will publish a pre-release of it and try it out here in this PR.

once that's all working, a pre-release of postcss-lit i think, so i can try it out in the wild.

[coveralls]

Pull Request Test Coverage Report for Build 3777392305

Warning: This coverage report may be inaccurate.

We've detected an issue with your CI configuration that might affect the accuracy of this pull request's coverage report. To ensure accuracy in future PRs, please see these guidelines. A quick fix for this PR: rebase it; your next report should be accurate.

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+3.3%) to 100.0%

---

Totals
Change from base Build 3622874084:	3.3%
Covered Lines:	305
Relevant Lines:	305

---

💛 - Coveralls

[43081j]

have published postcss-lit@next which seems to work! and came across some bugs i fixed while extracting all of this