netcode: rd3

Revert "feat: removed replicon + clientbound messages implemented, but untested"

This reverts commit 5ccd4fb282fe3858f302b284a4d985d590ac79a4.

feat: removed replicon + clientbound messages implemented, but untested

feat(netcode-rewrite): begin reimplementing replication

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

chore(netcode-rewrite): general codebase refactor