fixed small pagination issue in execute_pagination/added availability field in mongo schema

src/monitor_utils/models.py

@@ -54,6 +54,8 @@ class AvailabilityInfo:
         app_exclusive: Only purchasable through the retailer's app.
         member_pick: Flagged as a member pick offer.
         member_deal: Flagged as a member deal offer.
+        availability_last_checked: When available was last verified against
+            the retailer, letting monitors skip rechecks within an interval.
     """
 
     available: bool | None = None
@@ -61,6 +63,7 @@ class AvailabilityInfo:
     app_exclusive: bool | None = None
     member_pick: bool | None = None
     member_deal: bool | None = None
+    availability_last_checked: datetime | None = None
 
 
 @dataclass