DateTimeOffset Support

[cliedeman]

I found some notes on DateTimeOffset being removed due to ambiquity issues.
https://github.com/aloneguid/parquet-dotnet/releases/tag/4.3.0

Removing datetimeoffset from our models would be quite difficult.
What about the possiblity of adding a constrainted convesion thats expects UTC (or converts first to UTC) and always returns UTC.
Maintaining a second set of models just to convert DateTimeOffset to DateTime is currently the only option (if we want to use class serialization which we do)

This is simliar to the approach that grpc dotnets Timestamp takes - https://github.com/protocolbuffers/protobuf/blob/v27.1/csharp/src/Google.Protobuf/WellKnownTypes/TimestampPartial.cs#L125

I also considered removing all date time offest usage recently but ran into some ambiguity issues with DateTime - dotnet/efcore#4711 so neither approach is free of issues