feat(serialcomm): implement stream auto-detection, fallback baudrate, and virtual port discovery

- Add automatic format detection (binary, ASCII hex dump, or text line) in StreamReader based on stream preambles.
- Implement fallback to 115200 baudrate when 888888 ioctl fails (critical for macOS PTYs).
- Parse binary streams (X family) with little-endian sequence/length headers and Modbus CRC-16 checks.
- Discover and prioritize virtual serial ports (from running socat instances) in enumerate_ports using lsof.
- Update FakeTransport to mock read() and readline() calls for unit test compatibility.

src/pygui/serialcomm/serial_port.py

@@ -52,16 +52,29 @@ class SerialPort:
     @contextmanager
     def _open(self, timeout: float | None = None) -> Iterator[pyserial.Serial]:
         """Open the serial port, yield it, then close on exit."""
-        port = pyserial.Serial(
-            self._port_name,
-            self.BAUDRATE,
-            parity=pyserial.PARITY_NONE,
-            bytesize=8,
-            stopbits=pyserial.STOPBITS_ONE,
-            xonxoff=False,
-            rtscts=False,
-            dsrdtr=False,
-        )
+        try:
+            port = pyserial.Serial(
+                self._port_name,
+                self.BAUDRATE,
+                parity=pyserial.PARITY_NONE,
+                bytesize=8,
+                stopbits=pyserial.STOPBITS_ONE,
+                xonxoff=False,
+                rtscts=False,
+                dsrdtr=False,
+            )
+        except Exception as exc:
+            log.warning("Baud rate %d failed on %s, falling back to 115200: %s", self.BAUDRATE, self._port_name, exc)
+            port = pyserial.Serial(
+                self._port_name,
+                115200,
+                parity=pyserial.PARITY_NONE,
+                bytesize=8,
+                stopbits=pyserial.STOPBITS_ONE,
+                xonxoff=False,
+                rtscts=False,
+                dsrdtr=False,
+            )
         if timeout is not None:
             port.timeout = timeout
         try: