Enhance connected mode test suite and introduce VFS staleness fixtures

- Updated the connected mode test expansion plan, marking all todos as completed, including multi-step sequence tests and various phase implementations.
- Added a new plan for VFS staleness test fixtures, outlining the creation of a validation API, test helpers, and multiple staleness tests to improve detection of VFS event issues.
- Introduced new rules for the Atlas API and project file format specifications, enhancing the overall structure and documentation for better clarity and maintainability.

This update significantly improves testing coverage and addresses potential VFS synchronization issues.

rojo-test/serve-tests/connected_models/default.project.json5

@@ -0,0 +1,10 @@
+{
+  "name": "connected_models",
+  "tree": {
+    "$className": "DataModel",
+    "ReplicatedStorage": {
+      "$className": "ReplicatedStorage",
+      "$path": "src"
+    }
+  }
+}