(msgeditor): Support formatted timestamp.

src/utils/ui/msgeditor.py

@@ -54,7 +54,10 @@ class MsgEditor(MessageUI):
         By default, uses the provided `formatter` callback (if provided).
         """
         if self._formatter is not None:
-            await self._formatter(data)
+            return await self._formatter(data)
+        else:
+            return data
+
 
     def copy_data(self):
         return copy.deepcopy(self.history[-1])
@@ -78,7 +81,8 @@ class MsgEditor(MessageUI):
 
         if 'embed' in new_data:
             try:
-                discord.Embed.from_dict(new_data['embed'])
+                formatted_data = copy.deepcopy(new_data)
+                discord.Embed.from_dict(await self.format_data(formatted_data['embed']))
             except Exception as e:
                 raise UserInputError(
                     t(_p(
@@ -445,8 +449,17 @@ class MsgEditor(MessageUI):
                 embed_data.pop('footer', None)
 
             if (ts := timestamp_field.value):
+                if ts.isdigit():
+                    # Treat as UTC timestamp
+                    timestamp = dt.datetime.fromtimestamp(int(ts), dt.timezone.utc)
+                    ts = timestamp.isoformat()
+                    to_validate = ts
+                elif self._formatter:
+                    to_validate = await self._formatter(ts)
+                else:
+                    to_validate = ts
                 try:
-                    dt.datetime.fromisoformat(ts)
+                    dt.datetime.fromisoformat(to_validate)
                 except ValueError:
                     raise UserInputError(
                         t(_p(