Use existing attribute

`last_event_time` is set as a result of calling
`InfoRequest.find_in_state`. This commit adds an explicit accessor that
converts it to a `DateTime` and uses it in the view, preventing an extra
query for each `InfoRequest` in the result set.

Before:
Completed 200 OK in 14908.9ms (Views: 14625.3ms | ActiveRecord: 69.8ms)

After:
Completed 200 OK in 2481.0ms (Views: 2437.1ms | ActiveRecord: 5.2ms)

1 files changed, 9 insertions, 0 deletions

diff --git a/app/models/info_request.rb b/app/models/info_request.rb
index 0ca3a1279..b742dcc03 100644
--- a/app/models/info_request.rb
+++ b/app/models/info_request.rb
@@ -1383,6 +1383,15 @@ public
         end
     end
 
+    # The DateTime of the last InfoRequestEvent belonging to the InfoRequest
+    # Only available if the last_event_time attribute has been set. This is
+    # currentlt only set through .find_in_state
+    #
+    # Returns a DateTime
+    def last_event_time
+        attributes['last_event_time'].try(:to_datetime)
+    end
+
     private
 
     def set_defaults