feat!: examples on donglora 1.0 async API with shared _common helpers

Rewrite all scripts against the DongLoRa Protocol v2 async Dongle surface, and extract the shared MeshCore US preset into a single module.

* _common.py: MESHCORE_US preset (910.525 MHz / BW 62.5 / SF 7 / CR 4/5 / sync 0x1424 / 20 dBm) plus small helpers, imported by every example.

* New: explore.py, which prints the device capabilities and runs a single TX + RX roundtrip for quick hardware validation.

* simple_rx.py, simple_tx.py, ping_pong.py, lora_bridge.py all switch to donglora.Dongle and the new Modulation / LoRaConfig types.

* all_commands.py removed; it was an index of the old v0.1 command enum that no longer exists after the Protocol v2 split.

* justfile: drop stale recipes that referenced removed scripts.

simple_rx.py

@@ -1,39 +1,24 @@
 #!/usr/bin/env python3
-"""Receive LoRa packets and print them.
+"""Receive LoRa packets on the MeshCore US/Canada channel.
 
 Usage:
     python examples/simple_rx.py [PORT]
 """
 
-import contextlib
 import sys
 
-import serial
-
 import donglora as dl
+from _common import MESHCORE_US
 
-try:
-    ser = dl.connect(sys.argv[1] if len(sys.argv) > 1 else None)
-    print(dl.send(ser, "SetConfig", config=dl.DEFAULT_CONFIG))
-    print(dl.send(ser, "StartRx"))
+port = sys.argv[1] if len(sys.argv) > 1 else None
 
-    print("\nListening (Ctrl+C to stop)...\n")
-    ser.timeout = 1
-
-    while True:
-        data = dl.read_frame(ser)
-        if data is None:
-            continue
-        resp = dl.decode_response(data)
-        if resp["type"] == "RxPacket":
-            p = resp["payload"]
+with dl.connect(port, config=MESHCORE_US) as d:
+    print(f"Listening on {d.config.freq_hz / 1e6:.3f} MHz (Ctrl+C to stop)...\n")
+    try:
+        for pkt in d.rx():
             print(
-                f"  RSSI:{resp['rssi']:4d}dBm  SNR:{resp['snr']:3d}dB  len:{len(p):3d}  {p.hex()}"
+                f"  RSSI:{pkt.rssi_dbm:6.1f} dBm  SNR:{pkt.snr_db:5.1f} dB  "
+                f"len:{len(pkt.data):3d}  {pkt.data.hex()}"
             )
-except KeyboardInterrupt:
-    with contextlib.suppress(Exception):
-        dl.send(ser, "StopRx")
-    print("\nDone.")
-except serial.SerialException as e:
-    print(f"\nSerial error: {e}", file=sys.stderr)
-    sys.exit(1)
+    except KeyboardInterrupt:
+        print("\nDone.")