Initial implementation of custom price triggers

- likely to have some bugs, but this is good enough for a preview release.

token_bot/history_manager/history_manager.py

@@ -57,6 +57,16 @@ class HistoryManager:
                     await history.add_price(item)
                 self._history[flavor][region] = history
 
+    async def load_custom_alerts(self, custom_alerts: List[Alert]):
+        """Load custom price alerts and initialize their triggers with historical data."""
+        for alert in custom_alerts:
+            history = self._history[alert.flavor][alert.region]
+            # This will create the trigger on-demand via find_update_trigger_from_alert
+            trigger = await history.find_update_trigger_from_alert(alert)
+            # Process all historical data through this trigger to initialize its state
+            for datum in history.history:
+                trigger.check_and_update(datum, history.history)
+
     async def update_data(self, flavor: Flavor, region: Region) -> List[Alert]:
         history = self._history[flavor][region]
         current_price_data = await self._tdb.current(flavor)