Fix ANRs and concurrency issues during TTS initialization

[kreativityapps]

This patch addresses critical bugs in FlutterTtsPlugin’s cold-start path:

1. ConcurrentModificationException

Root cause:
Iterating pendingMethodCalls while clearing it under the same lock.

Fix:
Copy the list under synchronized, clear the original, then invoke the copy outside the lock.

2. ANRs on TextToSpeech.defaultVoice / getVoices() / setLanguage()

Root cause:
Binder IPC and Java deserialization (ObjectInputStream / Voice.) were happening synchronously on the main (UI) thread during OnInitListener.

Fix:
Call engineResult.success(1) (or .error()) immediately on the UI thread so Flutter is unblocked.
Spawn a short‐lived Thread { … } to perform all heavy TTS service calls (tts.defaultVoice, tts.setLanguage, voice enumeration) off the Looper.

Applied consistently in both onInitListenerWithCallback and onInitListenerWithoutCallback.

Had several ANR and crash reports:

🚨 Crash Report (click to expand)

Exception java.util.ConcurrentModificationException:
  at java.util.ArrayList$Itr.checkForComodification (ArrayList.java:1111)
  at java.util.ArrayList$Itr.next (ArrayList.java:1064)
  at com.tundralabs.fluttertts.FlutterTtsPlugin.onInitListener$lambda$3 (FlutterTtsPlugin.kt:221)
  at android.speech.tts.TextToSpeech.lambda$dispatchOnInit$0 (TextToSpeech.java:934)
  at android.speech.tts.TextToSpeech.$r8$lambda$y-uaMPlobiYouiY_T7xFoJSwPww (Unknown Source)
  at android.speech.tts.TextToSpeech$$ExternalSyntheticLambda13.run (D8$$SyntheticClass)
  at android.speech.tts.TextToSpeech.dispatchOnInit (TextToSpeech.java:943)
  at android.speech.tts.TextToSpeech.-$$Nest$mdispatchOnInit (Unknown Source)
  at android.speech.tts.TextToSpeech$Connection$SetupConnectionAsyncTask.onPostExecute (TextToSpeech.java:2324)
  at android.speech.tts.TextToSpeech$Connection$SetupConnectionAsyncTask.onPostExecute (TextToSpeech.java:2284)
  at android.os.AsyncTask.finish (AsyncTask.java:771)
  at android.os.AsyncTask.-$$Nest$mfinish (Unknown Source)
  at android.os.AsyncTask$InternalHandler.handleMessage (AsyncTask.java:788)
  at android.os.Handler.dispatchMessage (Handler.java:107)
  at android.os.Looper.loopOnce (Looper.java:249)
  at android.os.Looper.loop (Looper.java:337)
  at android.app.ActivityThread.main (ActivityThread.java:9486)
  at java.lang.reflect.Method.invoke
  at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run (RuntimeInit.java:636)
  at com.android.internal.os.ZygoteInit.main (ZygoteInit.java:1004)

🚨 ANR Report (click to expand)

    #00  pc 0x00000000004a67e4  /apex/com.android.art/lib64/libart.so (art::DumpNativeStack(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, int, BacktraceMap*, char const*, art::ArtMethod*, void*, bool)+140)
  

    #01  pc 0x00000000005b5704  /apex/com.android.art/lib64/libart.so (art::Thread::DumpStack(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, bool, BacktraceMap*, bool) const+372)
  

    #02  pc 0x00000000005d2ca4  /apex/com.android.art/lib64/libart.so (art::DumpCheckpoint::Run(art::Thread*)+924)
  

    #03  pc 0x00000000005b6670  /apex/com.android.art/lib64/libart.so (art::Thread::RunCheckpointFunction()+176)
  

    #04  pc 0x0000000000674160  /apex/com.android.art/lib64/libart.so (art::JniMethodFastEndWithReference(_jobject*, unsigned int, art::Thread*)+112)
  

    at dalvik.system.VMStack.getClosestUserClassLoader (Native method)
  

    at java.io.ObjectInputStream.latestUserDefinedLoader (ObjectInputStream.java:2186)
  

    at java.io.ObjectInputStream.resolveClass (ObjectInputStream.java:682)
  

    at android.os.Parcel$2.resolveClass (Parcel.java:3452)
  

    at java.io.ObjectInputStream.readNonProxyDesc (ObjectInputStream.java:1703)
  

    at java.io.ObjectInputStream.readClassDesc (ObjectInputStream.java:1594)
  

    at java.io.ObjectInputStream.readOrdinaryObject (ObjectInputStream.java:1872)
  

    at java.io.ObjectInputStream.readObject0 (ObjectInputStream.java:1412)
  

    at java.io.ObjectInputStream.readObject (ObjectInputStream.java:427)
  

    at android.os.Parcel.readSerializable (Parcel.java:3455)
  

    at android.os.Parcel.readSerializable (Parcel.java:3425)
  

    at android.speech.tts.Voice.<init> (Voice.java:86)
  

    at android.speech.tts.Voice.<init> (Voice.java:32)
  

    at android.speech.tts.Voice$1.createFromParcel (Voice.java:112)
  

    at android.speech.tts.Voice$1.createFromParcel (Voice.java:109)
  

    at android.os.Parcel.readTypedObject (Parcel.java:3119)
  

    at android.os.Parcel.createTypedArrayList (Parcel.java:2849)
  

    at android.speech.tts.ITextToSpeechService$Stub$Proxy.getVoices (ITextToSpeechService.java:1032)
  

    at android.speech.tts.TextToSpeech.getVoice (TextToSpeech.java:1699)
  

    at android.speech.tts.TextToSpeech.lambda$setLanguage$8$TextToSpeech (TextToSpeech.java:1527)
  

    at android.speech.tts.-$$Lambda$TextToSpeech$RsLPOHbMGtIthv7AyRho2VQZrE0.run (lambda)
  

    at android.speech.tts.TextToSpeech$Connection.runAction (TextToSpeech.java:2312)
  

    at android.speech.tts.TextToSpeech.runAction (TextToSpeech.java:791)
  

    at android.speech.tts.TextToSpeech.runAction (TextToSpeech.java:781)
  

    at android.speech.tts.TextToSpeech.setLanguage (TextToSpeech.java:1481)
  

    at com.tundralabs.fluttertts.FlutterTtsPlugin.firstTimeOnInitListener$lambda$5 (FlutterTtsPlugin.kt:263)
  

    at android.speech.tts.TextToSpeech.dispatchOnInit (TextToSpeech.java:863)
  

    at android.speech.tts.TextToSpeech.access$800 (TextToSpeech.java:77)
  

    at android.speech.tts.TextToSpeech$Connection$SetupConnectionAsyncTask.onPostExecute (TextToSpeech.java:2226)
  

    at android.speech.tts.TextToSpeech$Connection$SetupConnectionAsyncTask.onPostExecute (TextToSpeech.java:2181)
  

    at android.os.AsyncTask.finish (AsyncTask.java:771)
  

    at android.os.AsyncTask.access$900 (AsyncTask.java:199)
  

    at android.os.AsyncTask$InternalHandler.handleMessage (AsyncTask.java:788)
  

    at android.os.Handler.dispatchMessage (Handler.java:106)
  

    at android.os.Looper.loop (Looper.java:223)
  

    at android.app.ActivityThread.main (ActivityThread.java:7712)
  

    at java.lang.reflect.Method.invoke (Native method)
  

    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run (RuntimeInit.java:612)
  

    at com.android.internal.os.ZygoteInit.main (ZygoteInit.java:997)