fix(apple): resolve QoS priority inversions + two Swift concurrency warnings

Priority inversions (Thread Performance Checker): the Apple client drains every
plane on .userInteractive threads (video pump, audio, gamepad feedback) and
connects on a .userInitiated Task, but the connector's producer threads ran at
the default QoS — so a high-QoS consumer parked waiting on a lower-QoS producer.
Pin the connector's producers (outer worker thread, all tokio runtime threads via
on_thread_start, and the data-plane spawn_blocking pump) to .userInteractive on
Apple so they match the consumers. #[cfg(target_vendor = "apple")] helper using
the existing libc dep; no-op off Apple, no Swift-side change (no latency
regression).

GamepadFeedback.swift: the init's MainActor hop captured self implicitly-strong
while the inner $active sink captured it weakly — capture [weak self] in the hop
too (the sink stays weak to avoid the retain cycle).

StreamPump.swift: the @Sendable pump-thread closure captured the non-Sendable
AVSampleBufferDisplayLayer. enqueue/flush are documented thread-safe and only the
pump thread drives it after start(), so assert that with nonisolated(unsafe).

cargo build/test/clippy/fmt green (core + host); xcframework rebuilt; swift build
+ iOS/tvOS targets clean with both warnings gone. Runtime confirmation of the
inversion warnings needs a GUI run under Xcode's Thread Performance Checker.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

clients/apple/Sources/PunktfunkKit/GamepadFeedback.swift

@@ -173,7 +173,10 @@ public final class GamepadFeedback {
 
     public init(connection: PunktfunkConnection, manager: GamepadManager) {
         self.connection = connection
-        Task { @MainActor in
+        // Capture self weakly in the hop too, so the inner sink's weak capture isn't shadowing
+        // an implicit strong one — and the subscription (stored on self) never retain-cycles.
+        Task { @MainActor [weak self] in
+            guard let self else { return }
             self.activeSub = manager.$active.sink { [weak self] dc in
                 MainActor.assumeIsolated { self?.retarget(dc?.controller) }
             }