Fix caret display when cursor on embed line

lib/src/widgets/proxy.dart

@@ -103,8 +103,12 @@ class RenderEmbedProxy extends RenderProxyBox implements RenderContentProxyBox {
 
   @override
   Offset getOffsetForCaret(TextPosition position, Rect? caretPrototype) {
-    assert(position.offset <= 1 && position.offset >= 0);
+    assert(position.offset == 1 || position.offset == 0);
-    return position.offset == 0 ? Offset.zero : Offset(size.width, 0);
+    return position.offset == 0
+        ? Offset.zero
+        : Offset(
+            size.width - (caretPrototype == null ? 0 : caretPrototype.width),
+            0);
   }
 
   @override