fix: app freeze (ANR) when we check if a model has been downloaded (isModelDownloaded)

[helloimfrog]

I integrated google_mlkit_digital_ink_recognition into my app but it was freezed and caused ANR.
Tried with example app and have same result.
So I have a little changed on GenericModelManager, change the way to check if a model is downloaded by using Task callback (addOnSuccessListener and addOnFailureListener).
Seems it works correctly and won't cause ANR anymore.

[fbernaly]

@helloimfrog : thanks for the PR, will review

[Copilot]

Pull Request Overview

Refactors model download checking from synchronous to asynchronous to fix Android ANR (Application Not Responding) issues. The change replaces blocking Tasks.await() calls with proper callback-based async patterns using addOnSuccessListener and addOnFailureListener.

• Introduces a callback interface for asynchronous model download status checking
• Updates all ML Kit detector classes to use the new async model checking pattern
• Removes thread executor and blocking task operations that were causing ANR

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
GenericModelManager.java	Core refactor to async callback pattern, removes blocking executor operations
ObjectDetector.java	Updates remote object detection to use async model checking with inline processing
ImageLabelDetector.java	Updates remote image labeling to use async model checking with inline processing
DigitalInkRecognizer.java	Updates digital ink recognition to use async model checking pattern

Comments suppressed due to low confidence (1)

packages/google_mlkit_digital_ink_recognition/android/src/main/java/com/google_mlkit_digital_ink_recognition/DigitalInkRecognizer.java:73

• The entire recognition logic is now nested inside the callback, making the code deeply indented and harder to read. Consider extracting the recognition logic into a separate private method to improve readability and maintainability.

        genericModelManager.isModelDownloaded(
                model,
                new GenericModelManager.CheckModelIsDownloadedCallback() {
                    @Override
                    public void onModelDownloaded(Boolean isDownloaded) {
                        if (!isDownloaded) {
                            result.error("Model Error", "Model has not been downloaded yet ", null);
                            return;
                        }

                        String id = call.argument("id");
                        com.google.mlkit.vision.digitalink.DigitalInkRecognizer recognizer = instances.get(id);
                        if (recognizer == null) {
                            recognizer = DigitalInkRecognition.getClient(DigitalInkRecognizerOptions.builder(model).build());
                            instances.put(id, recognizer);
                        }

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[fbernaly]

@helloimfrog : could you address the comments by Copilot

[helloimfrog]

@fbernaly Checked all comments by Copilot and I pushed a little update. Please review again