fix(editor): onChange notification for flat model (#10589)

The primary purpose of this PR appears to be:
1. Simplifying the change notification API by removing the redundant value parameter from callbacks
2. Improving the reactive system's handling of specialized types (Text and Boxed) in flat data
3. Adding better test coverage for text handling in the flat data model

blocksuite/tests-legacy/e2e/utils/actions/misc.ts

@@ -146,6 +146,8 @@ export async function enterPlaygroundRoom(
         'Lit is in dev mode. Not recommended for production! See https://lit.dev/msg/dev-mode for more information.',
         // Figma embed:
         'Running frontend commit',
+        // Github timeout:
+        'Failed to load resource: the server responded with a status of 403',
       ].some(text => message.text().startsWith(text))
     ) {
       return;