Improve write speed by changing serialized data format

[gfs]

Is your feature request related to a problem? Please describe.
I suspect (requires benchmarking confirmation) that a large portion of the time spent for database writes is due to the json serialization of the object. We should explore the available serialization methods for C# and choose the fastest one - if there is a significant difference in practice.

Options:
MessagePack
Utf8json
Newtonsoft
System.text.json
Binary serialization