core: manual buffer sync with sync-rows, reuse unchanged buffers and pipelines across activations

Also lets the screenshot suite point at another reference directory and settle longer.

Amp-Thread-ID: https://ampcode.com/threads/T-01a0b2dd-db32-712d-99ce-12ce4a86d979
Co-authored-by: Heaust Azure <heaust.azure@gmail.com>

core/worker.js

@@ -34,6 +34,9 @@ addEventListener("message", async ({ data: message }) => {
         case "delete-object":
           core.delete_object(message.name, message.id);
           break;
+        case "sync-rows":
+          core.sync_rows(message.name, message.first ?? 0, message.count);
+          break;
         case "compile-graph":
           result = core.compile_graph(message.serialized);
           break;