PLT-5782 Restructure cardano-node-emulator API

[berewt]

Pre-submit checklist:

• Branch
  • [ ] Tests are provided (if possible)
  • [x] Commit sequence broadly makes sense
  • [x] Key commits have useful messages
  • [ ] Formatting, PNG optimization, etc. are updated
  • [ ] Important changes are reflected in changelog.d of the affected packages
• PR
  • [x] Self-reviewed the diff
  • [x] Useful pull request description
  • [ ] Reference the ADR in the PR and reference the PR in the ADR (if revelant)
  • [x] Reviewer requested

[koslambrou]

@berewt I can force-merge this one?