Fix: Android crash (NPE) on any BLE error — all onError callbacks pass null as the promise rejection code

[nas887]

Every onError callback in BlePlxModule.java calls: safePromise.reject(null, errorConverter.toJs(error));

The code parameter of PromiseImpl.reject is annotated @nonnull in the React Native bridge. Passing null bypasses the JS
error handler entirely and crashes the Android process with:

  java.lang.NullPointerException: Parameter specified as non-null is null:
    method com.facebook.react.bridge.PromiseImpl.reject, parameter code
    at com.bleplx.utils.SafePromise.reject(SafePromise.java:25)

This means any BLE error on Android is a fatal crash, not a catchable JS exception.

Fix: pass String.valueOf(error.errorCode.code) so the BleErrorCode integer (e.g. 401 for CharacteristicWriteFailed) is used as the rejection code, matching what the JS layer expects.