BluetoothSerialService class

A singleton service for managing Bluetooth serial communication and FHR data processing.

This class handles:

• Connecting and disconnecting to Bluetooth devices
• Receiving and parsing Bluetooth data packets
• Buffering and analyzing FHR (Fetal Heart Rate) data
• Streaming parsed FHR data to listeners
• Audio playback of decoded data using MyAudioTrack16Bit
• Enabling Bluetooth and retrieving paired devices

The service uses a broadcast Stream to provide real-time FHR data updates. It supports multiple data packet types and decodes them accordingly.

Example usage:

final bluetoothService = BluetoothSerialService();
await bluetoothService.connect(device);
bluetoothService.dataStream.listen((fhrData) { ... });