Add datetime utils to Entity

```
from datetime import datetime, timezone

class Entity:
    @classmethod
    def _check_datetime(cls, date_time: Any) -> datetime:
        return date_time if isinstance(date_time, datetime) else cls._time_aware_now()

    @staticmethod
    def _time_aware_now() -> datetime:
        return datetime.now(tz=timezone.utc)
```