feat: add support for getting a threads message (#598)

* feat: add support for getting a threads message

* refactor: use property not attribute

naff/models/discord/channel.py

@@ -1802,6 +1802,11 @@ def parent_channel(self) -> Union[GuildText, "GuildForum"]:
         """The channel this thread is a child of."""
         return self._client.cache.get_channel(self.parent_id)
 
+    @property
+    def parent_message(self) -> Optional["Message"]:
+        """The message this thread is a child of."""
+        return self._client.cache.get_message(self.parent_id, self.id)
+
     @property
     def mention(self) -> str:
         """Returns a string that would mention this thread."""

naff/models/discord/message.py

@@ -329,6 +329,11 @@ async def mention_roles(self) -> AsyncGenerator["models.Role", None]:
         for r_id in self._mention_roles:
             yield await self._client.cache.fetch_role(self._guild_id, r_id)
 
+    @property
+    def thread(self) -> "models.TYPE_THREAD_CHANNEL":
+        """The thread that was started from this message, if any"""
+        return self._client.cache.get_channel(self.id)
+
     async def fetch_referenced_message(self) -> Optional["Message"]:
         """
         Fetch the message this message is referencing, if any.