chore(java-sdk): refactor core interface to support stateless server-side api

[havenbarnes]

:bulb: Motivation and Context

#skip-changelog

This PR is the first of a handful of a refactor to allow the core Kotlin code to support stateless server-side Java applications, eventually adding a new version of the Java SDK into this repo just like https://github.com/PostHog/posthog-js-lite

Note: No functional changes to the Android SDK are expected with these changes

:green_heart: How did you test it?

No new server-side code here, so existing Android tests should suffice for confidence in these changes.

:pencil: Checklist

• [x] I reviewed the submitted code.
• [x] I added tests to verify the changes.
• [x] I updated the docs if needed.
• [x] No breaking change or entry added to the changelog.

[marandaneto]

since there will be multiple PRs, lets create a new branch? its likely a major bump.

[havenbarnes]

since there will be multiple PRs, lets create a new branch? its likely a major bump.

Good call, will start a chain yes

[marandaneto]

moving to draft since this is outdated

[marandaneto]

@dustinbyrne can we close this one now?