Add a codemod for dataclass changes in 3.11

[zsol]

Add a codemod for dataclass changes in 3.11

Python 3.11 changed the field default mutability check for dataclasses to only allow defaults which are hashable.

This codemod helps with the migration by changing all default values that aren't obviously hashable to use default_factory instead.

Note: it's impossible to accurately determine if a particular expression produces a hashable value in a codemod, so the codemod significantly over-approximates what's unhashable.

[zsol]

@itamaro no, not at all. If you wanna take a stab at it, feel free to commandeer this PR :)

[itamaro]

If you wanna take a stab at it, feel free to commandeer this PR :)

don't have the time right now, and it's useful enough to merge as is! we can iterate on it in future PRs.

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