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/screenshots/README.md

@@ -9,6 +9,11 @@ uses headed Chromium on a private Xvfb display and SwiftShader WebGPU at a fixed
 The first run downloads roughly 215 MB of GLBs into
 `~/.cache/yawn/gltf-sample-models`. Set `YAWN_GLTF_FIXTURES` to use another
 cache directory, or `YAWN_SCREENSHOT_MODELS=Box,BoomBox` to run a subset.
+`YAWN_SCREENSHOT_BASELINES` points at another reference directory (for example
+one captured from a known-good commit on a machine whose software renderer does
+not match the reviewed references), and `YAWN_SCREENSHOT_SETTLE_MS` (default
+1200) is how long the viewer gets to settle after the model loads before the
+capture; raise it on slow software renderers.
 Failed full-size captures and visual diffs are written to `output/`.
 
 To intentionally replace references after reviewing full-size renders, run:

addons/handles/test/screenshots/run.mjs

@@ -25,7 +25,10 @@ import { promisify } from "node:util";
 const execute = promisify(execFile);
 const directory = dirname(fileURLToPath(import.meta.url));
 const root = resolve(directory, "../../../..");
-const baselines = join(directory, "baselines");
+const baselines = resolve(
+  process.env.YAWN_SCREENSHOT_BASELINES ?? join(directory, "baselines"),
+);
+const settleMilliseconds = Number(process.env.YAWN_SCREENSHOT_SETTLE_MS ?? 1200);
 const output = resolve(
   process.env.YAWN_SCREENSHOT_OUTPUT ?? join(directory, "output"),
 );
@@ -44,7 +47,7 @@ const update = process.env.UPDATE_SCREENSHOTS === "1";
 const session = `yawn-gltf-screenshots-${process.pid}`;
 const temporary = await mkdtemp(join(tmpdir(), "yawn-gltf-screenshots-"));
 const imageSize = { width: 250, height: 180 };
-const allModels = (await readdir(baselines))
+const allModels = (await readdir(join(directory, "baselines")))
   .filter((name) => name.endsWith(".png") && name !== "initial.png")
   .map((name) => basename(name, ".png"))
   .sort()
@@ -366,7 +369,7 @@ for (const model of models) {
         );
         await browser("upload", "#file-picker", model.path);
         await browser("wait", "--fn", "window.__yawnScreenshotReady === true");
-        await browser("wait", "1200");
+        await browser("wait", String(settleMilliseconds));
 
         const state = await browser(
           "eval",