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

backend/app/schemas/session.py

@@ -2,6 +2,8 @@ from datetime import datetime
 from uuid import UUID
 from pydantic import BaseModel
 
+from app.util.encoders import force_utc_datetime
+
 
 class Session(BaseModel):
     id: UUID
@@ -9,4 +11,5 @@ class Session(BaseModel):
     last_used: datetime
 
     class Config:
-        from_attributes = True
+        from_attributes = True
+        json_encoders = {datetime: force_utc_datetime}