Add performance logging and background diagnostics

Performance Logging (Developer settings) logs a resource sample every 5s
in the foreground and background: CPU by area and thread, wakeups, GPU,
memory, disk, activity counters as rates (mpv property updates, player
time publishes, renders, saves, network, images, CloudKit events, log
entries, main run-loop wakeups), SwiftUI body evaluations of the player
views, and app/player/battery context. Each foreground/background
transition logs a summary of the period. MetricKit metrics and
diagnostics (CPU exceptions, hangs) are logged whenever logging is on.

Background diagnostics (iOS) log lifecycle, audio session and power
events with an app/player/render snapshot and a heartbeat that detects
suspension gaps and main-thread stalls. Logs are persisted per session
in Caches/Logs and the previous session is included in exports, so logs
survive the app being swiped away.

Yattee/Views/Player/PlayerControlsView.swift

@@ -198,6 +198,7 @@ struct PlayerControlsView: View {
     }
 
     var body: some View {
+        let _ = PerfCounter.body("PlayerControlsView")
         GeometryReader { geometry in
 
             ZStack {
@@ -1018,6 +1019,7 @@ struct PlayerControlsView: View {
 
     private var progressBar: some View {
         GeometryReader { geometry in
+            let _ = PerfCounter.body("PlayerControlsView.progressBar")
             ZStack(alignment: .bottomLeading) {
                 if playerState.isLive {
                     // For live streams, show simple red indicator (no scrubbing)