Fix the way cached presences work

There where various oddities and bugs here, namely:

- Guild kept its initial `presences` list even though this is basically
useless, and was never kept up-to-date
- State did not properly use all the fields of presence_update, and was
creating some annoying recursive oddities w/ user and presence binding

disco/gateway/events.py

@@ -153,6 +153,7 @@ class GuildCreate(GatewayEvent):
         and if None, this is a normal guild join event.
     """
     unavailable = Field(bool)
+    presences = ListField(Presence)
 
     @property
     def created(self):

disco/state.py

@@ -315,15 +315,30 @@ class State(object):
         self.guilds[event.guild_id].emojis = HashMap({i.id: i for i in event.emojis})
 
     def on_presence_update(self, event):
-        if event.user.id in self.users:
-            self.users[event.user.id].update(event.presence.user)
-            self.users[event.user.id].presence = event.presence
-            event.presence.user = self.users[event.user.id]
-
-        if event.guild_id not in self.guilds:
+        # Grab a copy of the user, and clear it out. All the operations below
+        #  do not want the nested user object, as the normaly structure is
+        #  user -> presence, and without clearing this becomes recursive
+        user = event.presence.user
+        user.presence = event.presence
+        event.presence.user = None
+
+        # if we have the user tracked locally, we can just use the presence
+        #  update to update both their presence and the cached user object.
+        if user.id in self.users:
+            self.users[user.id].update(user)
+        else:
+            # Otherwise this user does not exist in our local cache, so we can
+            #  use this opportunity to add them. They will quickly fall out of
+            #  scope and be deleted if they aren't used below
+            self.users[user.id] = user
+
+        # Some updates come with a guild_id and roles the user is in, we should
+        #  use this to update the guild member, but only if we have the guild
+        #  cached.
+        if event.roles is UNSET or event.guild_id not in self.guilds:
             return
 
-        if event.user.id not in self.guilds[event.guild_id].members:
+        if user.id not in self.guilds[event.guild_id].members:
             return
 
-        self.guilds[event.guild_id].members[event.user.id].user.update(event.user)
+        self.guilds[event.guild_id].members[user.id].roles = event.roles

disco/types/guild.py

@@ -9,7 +9,7 @@ from disco.util.functional import cached_property
 from disco.types.base import (
     SlottedModel, Field, ListField, AutoDictField, snowflake, text, binary, enum, datetime
 )
-from disco.types.user import User, Presence
+from disco.types.user import User
 from disco.types.voice import VoiceState
 from disco.types.channel import Channel
 from disco.types.message import Emoji
@@ -300,7 +300,6 @@ class Guild(SlottedModel, Permissible):
     emojis = AutoDictField(GuildEmoji, 'id')
     voice_states = AutoDictField(VoiceState, 'session_id')
     member_count = Field(int)
-    presences = ListField(Presence)
 
     synced = Field(bool, default=False)