fix(hci): Check stop flag periodically, even without incoming data

[wwaaijer]

Fixes stoprocent/noble#30 and stoprocent/bleno#11.

This adds a read timeout to the HCI Linux socket using SO_RCVTIMEO (see socket(7)), allowing the poll thread to check the stop flag even when there is no activity on the socket.

Alternatives considered:

• Immediate socket close - couldn't guarantee pending commands reach the HCI device
• Explicit wait for specific response events - would require significant additional code in both Bleno's and Noble's clean up process

Happy to discuss or elaborate!