Switch from synchronized mutations to copy-on-write (#609)

## Description
Instead of synchronizing all access to event observers, use a
`CopyOnWriteArrayList`. This means sending events doesn't need to lock.

app/src/main/java/com/github/damontecres/wholphin/util/mpv/MPVLib.kt

@@ -24,6 +24,7 @@ OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SO
 import android.content.Context
 import android.graphics.Bitmap
 import android.view.Surface
+import java.util.concurrent.CopyOnWriteArrayList
 
 // Wrapper for native library
 
@@ -96,115 +97,93 @@ object MPVLib {
         format: Int,
     )
 
-    private val observers = mutableListOf<EventObserver>()
+    private val observers = CopyOnWriteArrayList<EventObserver>()
 
     @JvmStatic
     fun addObserver(o: EventObserver) {
-        synchronized(observers) {
         observers.add(o)
     }
-    }
 
     @JvmStatic
     fun removeObserver(o: EventObserver) {
-        synchronized(observers) {
         observers.remove(o)
     }
-    }
 
     @JvmStatic
     fun eventProperty(
         property: String,
         value: Long,
     ) {
-        synchronized(observers) {
         for (o in observers) {
             o.eventProperty(property, value)
         }
     }
-    }
 
     @JvmStatic
     fun eventProperty(
         property: String,
         value: Boolean,
     ) {
-        synchronized(observers) {
         for (o in observers) {
             o.eventProperty(property, value)
         }
     }
-    }
 
     @JvmStatic
     fun eventProperty(
         property: String,
         value: Double,
     ) {
-        synchronized(observers) {
         for (o in observers) {
             o.eventProperty(property, value)
         }
     }
-    }
 
     @JvmStatic
     fun eventProperty(
         property: String,
         value: String,
     ) {
-        synchronized(observers) {
         for (o in observers) {
             o.eventProperty(property, value)
         }
     }
-    }
 
     @JvmStatic
     fun eventProperty(property: String) {
-        synchronized(observers) {
         for (o in observers) {
             o.eventProperty(property)
         }
     }
-    }
 
     @JvmStatic
     fun event(eventId: Int) {
-        synchronized(observers) {
         for (o in observers) {
             o.event(eventId)
         }
     }
-    }
 
     @JvmStatic
     fun eventEndFile(
         reason: Int,
         error: Int,
     ) {
-        synchronized(observers) {
         for (o in observers) {
             o.eventEndFile(reason, error)
         }
     }
-    }
 
-    private val log_observers = mutableListOf<LogObserver>()
+    private val log_observers = CopyOnWriteArrayList<LogObserver>()
 
     @JvmStatic
     fun addLogObserver(o: LogObserver) {
-        synchronized(log_observers) {
         log_observers.add(o)
     }
-    }
 
     @JvmStatic
     fun removeLogObserver(o: LogObserver) {
-        synchronized(log_observers) {
         log_observers.remove(o)
     }
-    }
 
     @JvmStatic
     fun logMessage(
@@ -212,12 +191,10 @@ object MPVLib {
         level: Int,
         text: String,
     ) {
-        synchronized(log_observers) {
         for (o in log_observers) {
             o.logMessage(prefix, level, text)
         }
     }
-    }
 
     interface EventObserver {
         fun eventProperty(property: String)