✨ Implement WebSocket API client

- List ports
- Read and write mute state
- Read and write volume

lib/mixer_state.dart

@@ -0,0 +1,108 @@
+// Converted with: https://app.quicktype.io/?l=dart
+
+import 'dart:convert';
+
+MixerState mixerStateFromJson(String str) =>
+    MixerState.fromJson(json.decode(str));
+
+String mixerStateToJson(MixerState data) => json.encode(data.toJson());
+
+class MixerState {
+  List<Port> inputs;
+  List<Port> outputs;
+
+  MixerState({
+    required this.inputs,
+    required this.outputs,
+  });
+
+  factory MixerState.fromJson(Map<String, dynamic> json) => MixerState(
+        inputs: List<Port>.from(json["inputs"].map((x) => Port.fromJson(x))),
+        outputs: List<Port>.from(json["outputs"].map((x) => Port.fromJson(x))),
+      );
+
+  Map<String, dynamic> toJson() => {
+        "inputs": List<dynamic>.from(inputs.map((x) => x.toJson())),
+        "outputs": List<dynamic>.from(outputs.map((x) => x.toJson())),
+      };
+}
+
+class Port {
+  String uuid;
+  String name;
+  Properties properties;
+  State state;
+  List<State> route;
+
+  Port({
+    required this.uuid,
+    required this.name,
+    required this.properties,
+    required this.state,
+    required this.route,
+  });
+
+  factory Port.fromJson(Map<String, dynamic> json) => Port(
+        uuid: json["UUID"],
+        name: json["name"],
+        properties: Properties.fromJson(json["properties"]),
+        state: State.fromJson(json["state"]),
+        route: List<State>.from(json["route"].map((x) => State.fromJson(x))),
+      );
+
+  Map<String, dynamic> toJson() => {
+        "UUID": uuid,
+        "name": name,
+        "properties": properties.toJson(),
+        "state": state.toJson(),
+        "route": List<dynamic>.from(route.map((x) => x.toJson())),
+      };
+}
+
+class Properties {
+  String backend;
+  int channels;
+
+  Properties({
+    required this.backend,
+    required this.channels,
+  });
+
+  factory Properties.fromJson(Map<String, dynamic> json) => Properties(
+        backend: json["backend"],
+        channels: json["channels"],
+      );
+
+  Map<String, dynamic> toJson() => {
+        "backend": backend,
+        "channels": channels,
+      };
+}
+
+class State {
+  String? toUuid;
+  bool mute;
+  double volume;
+  int balance;
+
+  State({
+    this.toUuid,
+    required this.mute,
+    required this.volume,
+    required this.balance,
+  });
+
+  factory State.fromJson(Map<String, dynamic> json) => State(
+        toUuid: json["toUUID"],
+        mute: json["mute"],
+        volume: json["volume"]?.toDouble(),
+        balance: json["balance"],
+      );
+
+  Map<String, dynamic> toJson() => {
+        "toUUID": toUuid,
+        "mute": mute,
+        "volume": volume,
+        "balance": balance,
+      };
+}