Do not reinvent DTOs with State object.

[proofit404]

Remove State, Argument, and Variable objects.

In all documentation examples use https://docs.python.org/3/library/types.html#types.SimpleNamespace instead.

Write documentation page how to use attrs and pydantic as DTOs with validation.

Field with init=False is a variable. Field with converter=DomainEntity, validator=TrafaretMapping is a contract.

Union features would be a separated library with attrs and pydantic libraries support.