Improve generic duck type programming with PartialMessageable

This adds jump_url, permissions_for, and created_at. Luckily, most
cases of this type being constructed already have the guild_id at
creation time.

discord/channel.py

@@ -2611,13 +2611,16 @@ class PartialMessageable(discord.abc.Messageable, Hashable):
     -----------
     id: :class:`int`
         The channel ID associated with this partial messageable.
+    guild_id: Optional[:class:`int`]
+        The guild ID associated with this partial messageable.
     type: Optional[:class:`ChannelType`]
         The channel type associated with this partial messageable, if given.
     """
 
-    def __init__(self, state: ConnectionState, id: int, type: Optional[ChannelType] = None):
+    def __init__(self, state: ConnectionState, id: int, guild_id: Optional[int] = None, type: Optional[ChannelType] = None):
         self._state: ConnectionState = state
         self.id: int = id
+        self.guild_id: Optional[int] = guild_id
         self.type: Optional[ChannelType] = type
 
     def __repr__(self) -> str:
@@ -2626,6 +2629,40 @@ class PartialMessageable(discord.abc.Messageable, Hashable):
     async def _get_channel(self) -> PartialMessageable:
         return self
 
+    @property
+    def jump_url(self) -> str:
+        """:class:`str`: Returns a URL that allows the client to jump to the channel."""
+        if self.guild_id is None:
+            return f'https://discord.com/channels/@me/{self.id}'
+        return f'https://discord.com/channels/{self.guild_id}/{self.id}'
+
+    @property
+    def created_at(self) -> datetime.datetime:
+        """:class:`datetime.datetime`: Returns the direct message channel's creation time in UTC."""
+        return utils.snowflake_time(self.id)
+
+    def permissions_for(self, obj: Any = None, /) -> Permissions:
+        """Handles permission resolution for a :class:`User`.
+
+        This function is there for compatibility with other channel types.
+
+        Since partial messageables cannot reasonably have the concept of
+        permissions, this will always return :meth:`Permissions.none`.
+
+        Parameters
+        -----------
+        obj: :class:`User`
+            The user to check permissions for. This parameter is ignored
+            but kept for compatibility with other ``permissions_for`` methods.
+
+        Returns
+        --------
+        :class:`Permissions`
+            The resolved permissions.
+        """
+
+        return Permissions.none()
+
     def get_partial_message(self, message_id: int, /) -> PartialMessage:
         """Creates a :class:`PartialMessage` from the message ID.