feat: post_create and post_generate hooks

[iloveitaly]

Description

Two additional hooks:

• post_create. Helpful for writing custom logic to run after a object is fully generated. There's not a great place to put this logic right now.
• post_generate. There are field-level post_generate methods, but nothing that can use the fully-generated model kwargs and run custom logic

I can write some additional tests for this, but wanted to get some initial feedback first.

[adhtruong]

Can the above functionality be achieved by overriding build and process_kwargs directly?

[iloveitaly]

Can the above functionality be achieved by overriding build and process_kwargs directly?

It can, but:

1. Overriding build requires you to call super() properly and type the params specific to the factory base class you are using
2. Overriding either of these requires understanding the internals of polyfactory. Using either of the proposed hooks requires no knowledge of polyfactory or changes as polyfactory continues to change
3. It's not self-documenting. Providing specific hooks makes it more clear exactly what you are trying to do

[adhtruong]

The above feels like could be handled with docs if wanted to handle that case? Not opposed to adding though depending what other @litestar-org/maintainers think.

[adhtruong]

Can this be called post_build? create is used to mean used with persistance handlers

[adhtruong]

Can this return the instance to be consistent with post_generate?

[adhtruong]

Do these need to be called on coverage methods too?