Add plugin to reduce client imports

[bombsimon]

• Convert input types and return types to ast.Constant
• Import TYPE_CHECKING and import types if set
• Import required types inside each method
• Add tests
• Update CHANGELOG
• Update README

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There are two generated clients to test this with as many permutations as possible both with and without ShorterResultsPlugin because it had a major effect on the result (and I had some bugs along the way). However the actual code is contained solely in ariadne_codegen/contrib.

This addresses one of the biggest issues from #233. Previously it was very slow to load the clients.py because all types used as input and return values were imported. This adds a plugin that converts them to ast.Constant and only imports the types if we're in a TYPE_CHECKING context.

Example from a project with a couple of hundred methods:

Before

>>> import time
>>> def load():
...     now = time.time()
...     import graphql_client.client
...     print(f"took {time.time() - now}")
...
>>> load()
took 5.043132305145264

After

>>> import time
>>> def load():
...     now = time.time()
...     import graphql_client.client
...     print(f"took {time.time() - now}")
...
>>> load()
took 0.14772796630859375

I wouldn't say it solves the issue because even if this improves imports of the client Pydantic v2 is still very slow. Loading some files with many classes can still take several seconds. I don't think we can solve this without rolling back to Pydantic v1 or wait for an upstream fix though.

[bombsimon]

I developed this plugin outside of ariadne-codegen so I didn't use any helpers to generate these. Tbh I don't think it helps, it just makes it tricker to read.

Let me know if you'd rather me to import and use all the generators even for plugins or if I can keep this as is.

[rafalp]

Just few nits for now.

[rafalp]

More nits but I think this will be good to merge after those.

[DamianCzajkowski]

LGTM!