fix(player): recover playback after a lost native-channel handoff

A player whose predecessor had not released the shared native channel
within three seconds skipped its own native dispose and chained its
release onto that predecessor. If the predecessor's teardown never
completed - one hung 4K session was enough - every later player waited
on the chain, failed to initialize, and playback stayed broken with
"Playback could not be started" until the app was killed.

Initialize and dispose now carry the creating instance's token. The
Android plugins remember which token created the current core and
acknowledge a dispose from any other token without touching the core,
so a dispose that lost the ownership race is provably stale and safe to
send. With that guard, a timed-out ownership wait force-disposes
instead of skipping, settles its release unchained, and frees the
channel for the next session; a dispose watchdog answers Dart even if
a native teardown hangs, leaking that one core instead of wedging all
future playback. Commands wait eight seconds (was three) so a slow but
healthy teardown delays the next session instead of failing it.

Verified on a Shield Pro: 38 back-to-back session races at 0.8-2.2s
gaps with zero failures and balanced teardowns, and a deep-link-over-
playback collision whose stale dispose is ignored, after which Back
returns to the still-playing session and Retry starts the new one.
Apple and desktop handlers ignore the token and keep the historical
skip semantics until they gain the guard.

android/app/src/test/kotlin/com/edde746/plezy/mpv/MpvPlayerPluginTest.kt

@@ -24,6 +24,7 @@ import java.util.concurrent.atomic.AtomicInteger
 import kotlinx.coroutines.suspendCancellableCoroutine
 import org.junit.Assert.assertEquals
 import org.junit.Assert.assertFalse
+import org.junit.Assert.assertNotNull
 import org.junit.Assert.assertNull
 import org.junit.Assert.assertTrue
 import org.junit.Test
@@ -632,6 +633,53 @@ class MpvPlayerPluginTest {
     assertEquals(0, pending.size)
   }
 
+  @Test
+  fun staleDisposeIsAcknowledgedWithoutTearingDownTheCore() {
+    // A dispose whose instanceId is not the core creator's lost the ownership
+    // race to a successor; tearing the core down anyway would kill that
+    // successor's session. It must be acknowledged as a no-op instead.
+    val plugin = MpvPlayerPlugin()
+    installCore(plugin, testCore { _, _ -> })
+    setPluginField(plugin, "coreInstanceId", 2L)
+    val result = RecordingResult()
+
+    plugin.onMethodCall(MethodCall("dispose", mapOf("instanceId" to 1)), result)
+    awaitCompletion(result)
+
+    assertNull(result.errorCode)
+    assertNotNull(getPluginField(plugin, "playerCore"))
+    assertEquals(2L, getPluginField(plugin, "coreInstanceId"))
+  }
+
+  @Test
+  fun matchingDisposeTearsDownTheCoreAndClearsTheToken() {
+    val plugin = MpvPlayerPlugin()
+    installCore(plugin, testCore { _, _ -> })
+    setPluginField(plugin, "coreInstanceId", 7L)
+    val result = RecordingResult()
+
+    plugin.onMethodCall(MethodCall("dispose", mapOf("instanceId" to 7)), result)
+    awaitCompletion(result)
+
+    assertNull(result.errorCode)
+    assertNull(getPluginField(plugin, "playerCore"))
+    assertNull(getPluginField(plugin, "coreInstanceId"))
+  }
+
+  @Test
+  fun tokenlessDisposeKeepsLegacySemanticsAndTearsDownTheCore() {
+    val plugin = MpvPlayerPlugin()
+    installCore(plugin, testCore { _, _ -> })
+    setPluginField(plugin, "coreInstanceId", 7L)
+    val result = RecordingResult()
+
+    plugin.onMethodCall(MethodCall("dispose", null), result)
+    awaitCompletion(result)
+
+    assertNull(result.errorCode)
+    assertNull(getPluginField(plugin, "playerCore"))
+  }
+
   @Test
   fun configDetachThenEngineDetachTearsDownVideoCoreAndPendingInitOnce() {
     val activity = Robolectric.buildActivity(Activity::class.java).setup().get()