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>

addons/handles/test/core-mock.ts

@@ -184,6 +184,10 @@ export class YawnCore {
     return Promise.resolve();
   }
 
+  syncRows() {
+    return Promise.resolve();
+  }
+
   array(name: string) {
     const rows = this.#arrays.get(name);
     if (!rows) throw new Error(`UNKNOWN_ARRAY: ${name}`);