[Bug] nativeStreamingInference() is not returned normally with BACKEND_MTK implementation

[htteng1976]

🐞 Bug Description

When testing LLMEngineService.generateStreamingResponse(), we found the nativeStreamingInference() is not returned normally.
We put a breakpoint at line #453 and didn't see the stop. That will make the resultFuture.complete() miss the invocation.

🎯 Steps to Reproduce

1. Setup NPU configuration in AppConstants.java (ex. BACKEND_DEFAULT, DEFAULT_LLM_MODEL)
2. Launch ChatActivit and enter prompt message: "你是誰"

📱 Test Device

Device: VIVO X200s
OS Version: Android 15
Screen Resolution: 2800 × 1260 pixels