[FR] Add __post_init__ equivalent

[Zocker1999NET]

It would be great to have something for Pony entities which works similar to the __post_init__ method for dataclasses, allowing to modify or further set up an entity object directly after it was created, without requiring to override Pony’s `init and then call it again with the same arguments.

This should be relatively easy to implement. However, while looking through Pony’s code, I don’t seem to get where this call should happen.

[JoshYuJump]

Maybe you can take a look at hooks
https://docs.ponyorm.org/api_reference.html#entity-hooks