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/Services/ImageLoading/ImageLoadingService.swift

@@ -127,4 +127,9 @@ private final class TokenStrippingPipelineDelegate: ImagePipelineDelegate {
         guard let url = request.url else { return nil }
         return ImageLoadingService.cacheKey(for: url)
     }
+
+    func imageTask(_ task: ImageTask, didCompleteWithResult result: Result<ImageResponse, ImagePipeline.Error>, pipeline _: ImagePipeline) {
+        guard PerfCounter.enabled, case let .success(response) = result else { return }
+        PerfCounter.count(response.cacheType == nil ? "image.loadFromNetwork" : "image.loadFromCache")
+    }
 }