Add buffering and cache length to stats

Model/Player/Backends/MPVBackend.swift

@@ -80,6 +80,14 @@ final class MPVBackend: PlayerBackend {
         client?.hwDecoder ?? "unknown"
     }
 
+    var bufferingState: Double {
+        client?.bufferingState ?? 0
+    }
+
+    var cacheDuration: Double {
+        client?.cacheDuration ?? 0
+    }
+
     init(model: PlayerModel, controls: PlayerControlsModel? = nil) {
         self.model = model
         self.controls = controls

Model/Player/Backends/MPVClient.swift

@@ -155,6 +155,14 @@ final class MPVClient: ObservableObject {
         mpv.isNil ? "unknown" : (getString("hwdec-current") ?? "unknown")
     }
 
+    var bufferingState: Double {
+        mpv.isNil ? 0.0 : getDouble("cache-buffering-state")
+    }
+
+    var cacheDuration: Double {
+        mpv.isNil ? 0.0 : getDouble("demuxer-cache-duration")
+    }
+
     var duration: CMTime {
         CMTime.secondsInDefaultTimescale(mpv.isNil ? -1 : getDouble("duration"))
     }