The [EncryptColumn] attribute cannot be used in netstandard 2.0 projects

[NinjaCross]

Often the data-models are not located into the same assembly that contains the DbContext.
That "datamodels assembly" usually tends to have a lower framework compatibility level (i.e. netstandard 2.0) than the assembly containing the DbContext (which have no less than net6.0).
In order to solve this problem, I suggest to move the attribute [EncryptColumn] (and other netstandard 2.0-compliant abstractions) into another, dedicated package "EntityFrameworkCore.EncryptColumn.Abstractions", and/or implement FluentAPI like suggested in #4