writeJson abstract method
Streaming JSON encoder (#lzdartstreamingjson): writes the canonical
JSON for this IpcMessage directly into sink, avoiding the
intermediate Map<String, Object> that toWire would produce and (for
the Snapshot / Delta / CrdtSync variants) recursing into the
payload's own writeJson so the per-batch allocations are eliminated
too. Byte-identical to jsonEncode(toWire()).
Implementation
void writeJson(StringSink sink);