feat: Display stickers in messages (#200)

This commit introduces the ability to display stickers within message bubbles.

Key changes:
- `Attachments.kt`: Added handling for `AttachmentType.STICKER`. If an attachment type is unsupported, a placeholder text is now displayed.
- `Sticker.kt`: New composable created to render `VkStickerDomain` using `AsyncImage`.
- `MessageBubble.kt`:
    - Adjusted background alpha for sticker messages to make the bubble transparent.
    - Minor refactoring of `minDateContainerWidth` and `dateContainerWidth` initialization.
- `VkStickerDomain.kt`: Added `getUrl()` function to construct sticker image URLs, with options for specifying width and background.

core/model/src/main/kotlin/dev/meloda/fast/model/api/domain/VkStickerDomain.kt

@@ -21,4 +21,12 @@ data class VkStickerDomain(
 
         return null
     }
+
+    fun getUrl(width: Int = 256, withBackground: Boolean = false): String? = when {
+        withBackground && backgroundImages != null -> {
+            backgroundImages.firstOrNull { it.width >= width }?.url
+        }
+        images != null -> images.firstOrNull { it.width >= width }?.url
+        else -> "https://vk.com/sticker/1-${id}-${width}b"
+    }
 }