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/desktopMain/kotlin/chat/simplex/common/platform/Images.desktop.kt

@@ -21,12 +21,19 @@ import kotlin.math.sqrt
 private fun errorBitmap(): ImageBitmap =
   ImageIO.read(ByteArrayInputStream(Base64.getMimeDecoder().decode("iVBORw0KGgoAAAANSUhEUgAAAEAAAABACAYAAACqaXHeAAAAAXNSR0IArs4c6QAAAKVJREFUeF7t1kENACEUQ0FQhnVQ9lfGO+xggITQdvbMzArPey+8fa3tAfwAEdABZQspQStgBssEcgAIkSAJkiAJljtEgiRIgmUCSZAESZAESZAEyx0iQRIkwTKBJEiCv5fgvTd1wDmn7QAP4AeIgA4oW0gJWgEzWCZwbQ7gAA7ggLKFOIADOKBMIAeAEAmSIAmSYLlDJEiCJFgmkARJkARJ8N8S/ADTZUewBvnTOQAAAABJRU5ErkJggg=="))).toComposeImageBitmap()
 
+private val base64BitmapCache = Collections.synchronizedMap(object : LinkedHashMap<String, ImageBitmap>(200, 0.75f, true) {
+  override fun removeEldestEntry(eldest: Map.Entry<String, ImageBitmap>): Boolean = size > 200
+})
+
 actual fun base64ToBitmap(base64ImageString: String): ImageBitmap {
+  base64BitmapCache[base64ImageString]?.let { return it }
   val imageString = base64ImageString
     .removePrefix("data:image/png;base64,")
     .removePrefix("data:image/jpg;base64,")
   return try {
-    ImageIO.read(ByteArrayInputStream(Base64.getMimeDecoder().decode(imageString))).toComposeImageBitmap()
+    ImageIO.read(ByteArrayInputStream(Base64.getMimeDecoder().decode(imageString))).toComposeImageBitmap().also {
+      base64BitmapCache[base64ImageString] = it
+    }
   } catch (e: Throwable) {
     Log.e(TAG, "base64ToBitmap error: $e")
     errorBitmap()

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

@@ -2,6 +2,7 @@ package chat.simplex.common.views.chat.item
 
 import androidx.compose.runtime.Composable
 import androidx.compose.ui.graphics.*
+import androidx.compose.ui.graphics.painter.BitmapPainter
 import androidx.compose.ui.graphics.painter.Painter
 import chat.simplex.common.model.CIFile
 import chat.simplex.common.platform.*
@@ -17,7 +18,7 @@ actual fun SimpleAndAnimatedImageView(
   ImageView: @Composable (painter: Painter, onClick: () -> Unit) -> Unit
 ) {
   // LALAL make it animated too
-  ImageView(imageBitmap.toAwtImage().toPainter()) {
+  ImageView(BitmapPainter(imageBitmap)) {
     if (getLoadedFilePath(file) != null) {
       ModalManager.fullscreen.showCustomModal(animated = false) { close ->
         ImageFullScreenView(imageProvider, close)

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

@@ -16,6 +16,7 @@ import kotlinx.coroutines.delay
 import java.io.ByteArrayInputStream
 import java.io.File
 import java.net.URI
+import java.util.*
 import javax.imageio.ImageIO
 import kotlin.io.encoding.Base64
 import kotlin.io.encoding.ExperimentalEncodingApi
@@ -128,6 +129,14 @@ actual fun getAppFileUri(fileName: String): URI {
   }
 }
 
+private val loadedImageCache = Collections.synchronizedMap(object : LinkedHashMap<String, Pair<ImageBitmap, ByteArray>>(30, 0.75f, true) {
+  override fun removeEldestEntry(eldest: Map.Entry<String, Pair<ImageBitmap, ByteArray>>): Boolean = size > 30
+})
+
+actual fun clearImageCaches() {
+  loadedImageCache.clear()
+}
+
 actual suspend fun getLoadedImage(file: CIFile?): Pair<ImageBitmap, ByteArray>? {
   var filePath = getLoadedFilePath(file)
   if (chatModel.connectedToRemote() && filePath == null) {
@@ -135,10 +144,10 @@ actual suspend fun getLoadedImage(file: CIFile?): Pair<ImageBitmap, ByteArray>?
     filePath = getLoadedFilePath(file)
   }
   return if (filePath != null) {
-    try {
+    loadedImageCache[filePath] ?: try {
       val data = if (file?.fileSource?.cryptoArgs != null) readCryptoFile(filePath, file.fileSource.cryptoArgs) else File(filePath).readBytes()
       val bitmap = getBitmapFromByteArray(data, false)
-      if (bitmap != null) bitmap to data else null
+      if (bitmap != null) (bitmap to data).also { loadedImageCache[filePath] = it } else null
     } catch (e: Exception) {
       Log.e(TAG, "Unable to read crypto file: " + e.stackTraceToString())
       null