Make transaction.meter_end required and force tz utc for all datetimes

backend/app/util/encoders.py

@@ -1,3 +1,4 @@
+from datetime import datetime, timezone
 from decimal import Decimal
 from typing import Union
 
@@ -19,4 +20,8 @@ def decimal_encoder(dec_value: Decimal) -> Union[int, float]:
     if isinstance(exponent, int) and exponent >= 0:
         return int(dec_value)
     else:
-        return float(dec_value)
+        return float(dec_value)
+    
+def force_utc_datetime(datetime_value: datetime) -> datetime:
+    """Force a datetime to be in the UTC timzone"""
+    return datetime_value.replace(tzinfo=timezone.utc)