[Performance] Optimize queries in conversation/message finders (#364)

* [Performance] Optimize queries in conversation/message finders

* Add message_finder spec

* Fix message_finder spec

app/finders/conversation_finder.rb

@@ -66,7 +66,9 @@ class ConversationFinder
   end
 
   def find_all_conversations
-    @conversations = current_account.conversations.where(inbox_id: @inbox_ids)
+    @conversations = current_account.conversations.includes(
+      :assignee, :contact, :inbox
+    ).where(inbox_id: @inbox_ids)
   end
 
   def filter_by_assignee_type

app/finders/message_finder.rb

@@ -10,10 +10,14 @@ class MessageFinder
 
   private
 
-  def messages
-    return @conversation.messages if @params[:filter_internal_messages].blank?
+  def conversation_messages
+    @conversation.messages.includes(:attachment, user: { avatar_attachment: :blob })
+  end
 
-    @conversation.messages.where.not('private = ? OR message_type = ?', true, 2)
+  def messages
+    return conversation_messages if @params[:filter_internal_messages].blank?
+
+    conversation_messages.where.not('private = ? OR message_type = ?', true, 2)
   end
 
   def current_messages