feat: add a provider for mpris data

src/provider/Player.qml

@@ -0,0 +1,22 @@
+pragma Singleton
+
+import Quickshell
+import Quickshell.Services.Mpris
+import QtQuick
+
+Singleton {
+    id: player
+    property MprisPlayer current: player.all[player.index]
+    property var all: Mpris.players.values
+    property int index: Mpris.players.values.findIndex(p => p.playbackState === MprisPlaybackState.Playing)
+
+    property var next: () => {
+        player.index = (player.index + 1) % all.length;
+    }
+    property var prev: () => {
+        const newInd = player.index - 1;
+        player.index = newInd < 0 ? all.length - 1 : newInd;
+    }
+
+    property bool isPlaying: current?.playbackState === MprisPlaybackState.Playing
+}