Date
Custom serializer for Date objects to convert them into String during serialization and back to Date during deserialization. Needed for Firestore integration
The serializer stores the Date as a string representing the time in milliseconds since the epoch.
Example: Date("2021-12-31T12:59:59") will be serialized to "1638364799000".
This serializer is used by BiWeeklyEvaluationEntry to handle the dateCompleted property.