chore(netcode-rewrite): further code cleanup & simplification

chore(netcode-rewrite): general codebase refactor

feat(netcode-rewrite): miscellaneous fixes

fix: planets rely purely on springs now, so it should be possible to push them around now

feat: avian f64, which means orbit springs work now

fix: parts have initial velocity matching parent planet, and orbit indicator uses relative velocity

feat: orbits