Complete todos for stress tests and add syncback_stress fixture

- Marked all todos in the stress test plan as completed, including the implementation of timing helpers, a PRNG, and various fuzz tests for two-way sync operations.
- Introduced a new `syncback_stress` fixture with a project configuration and multiple Luau modules (Alpha, Bravo, Charlie, Delta, Echo) to support stress testing.
- Enhanced the `api.rs` file with improved path handling logic for better integration with the stress testing framework.

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

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