Add web serial support and USB tests

lib/utils/usb_port_labels.dart

@@ -0,0 +1,57 @@
+const String usbRequestPortLabel = 'Choose USB Device';
+
+String normalizeUsbPortName(String portLabel) {
+  final separatorIndex = portLabel.indexOf(' - ');
+  final normalized = separatorIndex >= 0
+      ? portLabel.substring(0, separatorIndex)
+      : portLabel;
+  return normalized.trim();
+}
+
+String friendlyUsbPortName(String portLabel) {
+  final separatorIndex = portLabel.indexOf(' - ');
+  if (separatorIndex < 0) {
+    return portLabel.trim();
+  }
+  final friendlyName = portLabel.substring(separatorIndex + 3).trim();
+  if (friendlyName.isEmpty) {
+    return normalizeUsbPortName(portLabel);
+  }
+  return friendlyName;
+}
+
+String describeWebUsbPort({
+  required int? vendorId,
+  required int? productId,
+  Map<String, String> knownUsbNames = const <String, String>{},
+}) {
+  if (vendorId == null && productId == null) {
+    return usbRequestPortLabel;
+  }
+
+  final vendorHex = vendorId?.toRadixString(16).padLeft(4, '0').toUpperCase();
+  final productHex = productId?.toRadixString(16).padLeft(4, '0').toUpperCase();
+  final knownName = (vendorHex != null && productHex != null)
+      ? knownUsbNames['${vendorHex.toLowerCase()}:${productHex.toLowerCase()}']
+      : null;
+
+  final parts = <String>[knownName ?? 'Web Serial Device'];
+  if (vendorHex != null) {
+    parts.add('VID:$vendorHex');
+  }
+  if (productHex != null) {
+    parts.add('PID:$productHex');
+  }
+  return '${parts.first} (${parts.skip(1).join(' ')})';
+}
+
+String buildUsbDisplayLabel({
+  required String basePortLabel,
+  String? deviceName,
+}) {
+  final trimmedName = deviceName?.trim() ?? '';
+  if (trimmedName.isEmpty) {
+    return basePortLabel;
+  }
+  return '$basePortLabel - $trimmedName';
+}