fix(macos): unbound the AVFoundation AO's PCM lookahead

MPVKit 1.0.15 bounded how far ahead ao_avfoundation enqueues PCM on macOS —
about 450ms of queue against the renderer's own ~1.7s — and disarms the feed
between refills, re-arming from a half-bound timer. 2.10 is the first release
to carry it: the AO pin went 1.0.12 to 1.0.16 over that release. #1711 reports
macOS audio skipping roughly every half second on 2.10 that 2.9.1 does not
have, and that bound is the only change to this path in the window, so restore
the renderer-owned depth 2.9.1 shipped. The option documents 0 as exactly that.

The AO itself stays. allowedAudioSpatializationFormats is a property of
AVSampleBufferAudioRenderer, and the compressed E-AC3 JOC sink lives there
too, while ao_coreaudio drives the HAL device and exposes no spatialization
control at all — CoreAudio is the fallback, not an alternative.

The cost is the latency the bound was added to remove: mpv multiplies --volume
into the samples as it hands them over, so a volume change stays inaudible
until the renderer queue drains. That is 2.9.1's behaviour, and the fix for it
belongs to the AO's gain domain rather than to how far ahead it may buffer.

Verified against the pinned MPVKit 1.0.16 libmpv on macOS: both option writes
are accepted, playback lands on ao_avfoundation and advances at 0.997x real
time. Runner's native suite passes.

macos/Runner/MpvPlayer/MpvPlayerCore.swift

@@ -102,7 +102,21 @@ class MpvPlayerCore: MpvPlayerCoreBase {
   }
 
   override func configurePlatformMpvOptions(mpv: OpaquePointer) {
+    // AVFoundation stays the macOS output. Spatialization is only reachable
+    // through the AVFoundation renderer — allowedAudioSpatializationFormats is a
+    // property of AVSampleBufferAudioRenderer (macOS 12+), and the AO opts
+    // compressed playback into the multichannel format — and the E-AC3 JOC sink
+    // lives there too. CoreAudio writes straight to the HAL device and exposes no
+    // spatialization control at all, so it is a fallback, not an alternative.
     checkError(mpv_set_option_string(mpv, "ao", "avfoundation,coreaudio"))
+    // Unbound the AO's PCM lookahead, restoring the renderer-owned queue depth
+    // 2.9.1 shipped (#1711). The macOS-only 0.5s bound MPVKit 1.0.15 added is the
+    // only change to this path between 2.9.1 and 2.10, and 2.10 skips audio at
+    // roughly that cadence. Its purpose was making mpv's software --volume, which
+    // is baked into the samples handed to the AO, audible before the queue
+    // drains; that latency is back, and belongs to the AO's gain domain rather
+    // than to how far ahead it may buffer.
+    checkError(mpv_set_option_string(mpv, "ao-avfoundation-max-lookahead", "0"))
   }
 
   func reattachMetalLayer() {