scanner: unbind CameraX on PlatformView dispose (Android)

dispose() only shut down the analysis executor, leaving the camera
bound to the activity LifecycleOwner so the indicator stayed on after
the scan page popped. Hold the ProcessCameraProvider, unbindAll() in
dispose, and guard the async bind callback so we don't rebind after
dispose.

android/src/main/kotlin/io/swipelab/ux/ScannerPlugin.kt

@@ -171,6 +171,8 @@ private class ScannerPlatformView(
             ),
         )
     }
+    private var cameraProvider: ProcessCameraProvider? = null
+    private var disposed = false
 
     init {
         if (lifecycleOwner != null) bindCamera(context, lifecycleOwner)
@@ -179,7 +181,9 @@ private class ScannerPlatformView(
     private fun bindCamera(context: Context, lifecycleOwner: LifecycleOwner) {
         val cameraProviderFuture = ProcessCameraProvider.getInstance(context)
         cameraProviderFuture.addListener({
-            val cameraProvider = cameraProviderFuture.get()
+            if (disposed) return@addListener
+            val provider = cameraProviderFuture.get()
+            cameraProvider = provider
 
             val preview = Preview.Builder().build().also {
                 it.setSurfaceProvider(previewView.surfaceProvider)
@@ -191,8 +195,8 @@ private class ScannerPlatformView(
                 .also { it.setAnalyzer(analysisExecutor, ::analyze) }
 
             try {
-                cameraProvider.unbindAll()
-                cameraProvider.bindToLifecycle(
+                provider.unbindAll()
+                provider.bindToLifecycle(
                     lifecycleOwner,
                     CameraSelector.DEFAULT_BACK_CAMERA,
                     preview,
@@ -238,6 +242,9 @@ private class ScannerPlatformView(
     override fun getView(): View = previewView
 
     override fun dispose() {
+        disposed = true
+        cameraProvider?.unbindAll()
+        cameraProvider = null
         analysisExecutor.shutdown()
     }
 }