ET 0.7 updates

[kirklandsign]

• API change:
  • in LlmCallback, public void onStats(float tps) -> public void onStats(String tps) , where it's a json. You can calculate the tps like https://github.com/pytorch/executorch/blob/e609943eeda04f966aea174f460309cbf22e3913/extension/benchmark/android/benchmark/app/src/main/java/org/pytorch/minibench/LlmBenchmarkActivity.java#L86-L94