Adds a hand-rolled RFC 6455 WS client and minimal JSON codec to common/ (no
third-party deps, keeping legacy ForgeGradle's classpath untouched), a
DefaultBackendConnection implementing hello/hello_ack auth and reconnect
with backoff, and Forge1122ChunkAdapter deriving top-of-column state from
the vanilla heightmap for both initial chunk backfill and event-driven
deltas (block break/place, deferred one tick to read post-mutation state).
MCMapperMod wires it up with config-driven backendUrl/serverToken and a
tick-based flush batch. Verified against a live MCMapper-Backend api
instance (real WS handshake, hello_ack, and 256-column batch landing
correctly in Postgres).