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/lib.rs

@@ -186,6 +186,20 @@ impl Core {
         Ok(())
     }
 
+    /// Uploads rows `first .. first + count` of `name` to every active GPU buffer bound to it.
+    pub fn sync_rows(&self, name: &str, first: u32, count: u32) -> Result<(), JsError> {
+        let gpu = self.gpu.borrow();
+        let gpu = gpu
+            .as_ref()
+            .ok_or_else(|| JsError::new("WEBGPU_UNINITIALIZED"))?;
+        self.store
+            .borrow()
+            .sync_rows(name, first, count, gpu, &self.data.borrow())
+            .map_err(|error| JsError::new(&error))?;
+        self.data.borrow_mut().mark_dirty();
+        Ok(())
+    }
+
     pub fn compile_graph(&self, source: &str) -> Result<String, JsError> {
         let graph = compiler::compile(source).map_err(JsError::new)?;
         Ok(self.store.borrow_mut().save(graph))