ObjectExtensions should be internal

[neman]

ObjectExtensions class (https://github.com/Data-Tech-International/TaxCore-Libraries/tree/main/src/Certificates/Extensions) should be internal.

It should be only used by Certificates and not other external code.

At this moment there is possibility of using this code through reference.

And for the future, TaxCore Libraries should be expanded with new project Extensions.Primitives or similar and use it across entire code base.