maxWriteWithoutResponseSize conformance test

Targeted conformance for BluetoothRemoteGATTCharacteristic.maxWriteWithoutResponseSize

Runs an explicit pass/fail check sequence against the new attribute added by CL 7879985. The getter is synchronous and should reflect the current ATT_MTU minus 3.

Required launch flag:

--enable-features=NewBLEGattSessionHandling,WebBluetooth

Requires the dino tester ESP32-C3 firmware advertising on FFE0/FFE1.