multiplatform: fix image loading performance and layout stability (#6631)

- Replace runBlocking { imageAndFilePath(file) } with LaunchedEffect +
  withContext(Dispatchers.IO) to unblock main thread on all platforms
- Set fixed container size (width + aspectRatio) from preview bitmap to
  eliminate layout shifts during async image loading
- Cache base64ToBitmap() with remember() in CIImageView and FramedItemView
- Desktop: replace imageBitmap.toAwtImage().toPainter() with BitmapPainter
  to eliminate unnecessary round-trip conversion
- Desktop: add LRU cache for base64ToBitmap (200 entries) and
  getLoadedImage (30 entries) to survive LazyColumn item disposal
- Clear loaded image cache on app file deletion via expect/actual

Co-authored-by: Evgeny Poberezkin <evgeny@poberezkin.com>

apps/multiplatform/common/src/commonMain/kotlin/chat/simplex/common/views/chat/item/CIImageView.kt

@@ -26,7 +26,7 @@ import chat.simplex.common.ui.theme.DEFAULT_MAX_IMAGE_WIDTH
 import chat.simplex.common.views.chat.chatViewScrollState
 import chat.simplex.res.MR
 import dev.icerock.moko.resources.StringResource
-import kotlinx.coroutines.runBlocking
+import kotlinx.coroutines.*
 
 @Composable
 fun CIImageView(
@@ -38,6 +38,7 @@ fun CIImageView(
   receiveFile: (Long) -> Unit
 ) {
   val blurred = remember { mutableStateOf(appPrefs.privacyMediaBlurRadius.get() > 0) }
+  val previewBitmap = remember(image) { base64ToBitmap(image) }
   @Composable
   fun progressIndicator() {
     CircularProgressIndicator(
@@ -144,7 +145,7 @@ fun CIImageView(
         .privacyBlur(!smallView, blurred, scrollState = chatViewScrollState.collectAsState(), onLongClick = { showMenu.value = true }),
         contentAlignment = Alignment.Center
       ) {
-        imageView(base64ToBitmap(image), onClick = {
+        imageView(previewBitmap, onClick = {
           if (fileSource != null) {
             openFile(fileSource)
           }
@@ -178,14 +179,16 @@ fun CIImageView(
 
   Box(
     Modifier.layoutId(CHAT_IMAGE_LAYOUT_ID)
+      .then(
+        if (!smallView) {
+          val w = if (previewBitmap.width * 0.97 <= previewBitmap.height) imageViewFullWidth() * 0.75f else DEFAULT_MAX_IMAGE_WIDTH
+          Modifier.width(w).aspectRatio(previewBitmap.width.toFloat() / previewBitmap.height.toFloat())
+        } else Modifier
+      )
       .desktopModifyBlurredState(!smallView, blurred, showMenu),
     contentAlignment = Alignment.TopEnd
   ) {
-    val res: MutableState<Triple<ImageBitmap, ByteArray, String>?> = remember {
-      mutableStateOf(
-        if (chatModel.connectedToRemote()) null else runBlocking { imageAndFilePath(file) }
-      )
-    }
+    val res: MutableState<Triple<ImageBitmap, ByteArray, String>?> = remember { mutableStateOf(null) }
     if (chatModel.connectedToRemote()) {
       LaunchedEffect(file, CIFile.cachedRemoteFileRequests.toList()) {
         withBGApi {
@@ -195,9 +198,9 @@ fun CIImageView(
         }
       }
     } else {
-      KeyChangeEffect(file) {
+      LaunchedEffect(file) {
         if (res.value == null || res.value!!.third != getLoadedFilePath(file)) {
-          res.value = imageAndFilePath(file)
+          res.value = withContext(Dispatchers.IO) { imageAndFilePath(file) }
         }
       }
     }
@@ -206,7 +209,7 @@ fun CIImageView(
       val (imageBitmap, data, _) = loaded
       SimpleAndAnimatedImageView(data, imageBitmap, file, imageProvider, smallView, @Composable { painter, onClick -> ImageView(painter, image, file.fileSource, onClick) })
     } else {
-      imageView(base64ToBitmap(image), onClick = {
+      imageView(previewBitmap, onClick = {
         if (file != null) {
           when {
             file.fileStatus is CIFileStatus.RcvInvitation || file.fileStatus is CIFileStatus.RcvAborted ->

apps/multiplatform/common/src/commonMain/kotlin/chat/simplex/common/views/chat/item/FramedItemView.kt

@@ -144,7 +144,7 @@ fun FramedItemView(
           Box(Modifier.fillMaxWidth().weight(1f)) {
             ciQuotedMsgView(qi)
           }
-          val imageBitmap = base64ToBitmap(qi.content.image)
+          val imageBitmap = remember(qi.content.image) { base64ToBitmap(qi.content.image) }
           Image(
             imageBitmap,
             contentDescription = stringResource(MR.strings.image_descr),
@@ -156,7 +156,7 @@ fun FramedItemView(
           Box(Modifier.fillMaxWidth().weight(1f)) {
             ciQuotedMsgView(qi)
           }
-          val imageBitmap = base64ToBitmap(qi.content.image)
+          val imageBitmap = remember(qi.content.image) { base64ToBitmap(qi.content.image) }
           Image(
             imageBitmap,
             contentDescription = stringResource(MR.strings.video_descr),

apps/multiplatform/common/src/commonMain/kotlin/chat/simplex/common/views/helpers/Utils.kt

@@ -130,6 +130,8 @@ const val MAX_FILE_SIZE_LOCAL: Long = Long.MAX_VALUE
 
 expect fun getAppFileUri(fileName: String): URI
 
+expect fun clearImageCaches()
+
 // https://developer.android.com/training/data-storage/shared/documents-files#bitmap
 expect suspend fun getLoadedImage(file: CIFile?): Pair<ImageBitmap, ByteArray>?
 
@@ -423,6 +425,7 @@ fun deleteAppFiles() {
   } catch (e: java.lang.Exception) {
     Log.e(TAG, "Util deleteAppFiles error: ${e.stackTraceToString()}")
   }
+  clearImageCaches()
 }
 
 fun directoryFileCountAndSize(dir: String): Pair<Int, Long> { // count, size in bytes