backend: move NetworkBackend and ABackend into backend/ folder

- network_backend.py -> backend/network.py
- a_backend.py -> backend/a_backend.py
- update all imports accordingly

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/network.py

@@ -6,7 +6,7 @@ from queue import Queue
 from msg.container import MsgContainer
 from transceiver import Transceiver, ATransceiver
 
-from a_backend import ABackend
+from backend.a_backend import ABackend
 
 
 class NetworkBackend(ABackend):

gui/backends.py

@@ -8,7 +8,7 @@ for _p in [_root, _gui]:
     if _p not in sys.path:
         sys.path.insert(0, _p)
 
-from a_backend     import ABackend
+from backend.a_backend import ABackend
 from a_transceiver import ATransceiver
 from msg.container import MsgContainer
 

gui/data_model.py

@@ -11,7 +11,7 @@ for _p in [_root, _gui]:
 from transceiver import Transceiver
 from nmea.packetizer import NmeaPacketizer
 from ubx.packetizer import UbxPacketizer
-from network_backend import NetworkBackend
+from backend.network import NetworkBackend
 from ubx.ubx import frame_create
 
 GNSS_NAMES = {

main.py

@@ -2,7 +2,7 @@ import time
 import signal
 import argparse
 
-from network_backend import NetworkBackend
+from backend.network import NetworkBackend
 from msg.frame_logger import FrameLogger
 from transceiver import Transceiver
 

transceiver.py

@@ -1,7 +1,7 @@
 from a_transceiver import ATransceiver
 from msg.container import MsgContainer
 from msg.talker import MsgTalker
-from a_backend import ABackend
+from backend.a_backend import ABackend
 
 
 class Transceiver(ATransceiver, MsgTalker):