Co-authored-by: Daniel Kjellid <42611331+danielkjellid@users.noreply.github.com>

* Fix X | Y union syntax breaks GenericModel (#4146)

* Update changes/4146-thenx.md

Co-authored-by: ⬢ Samuel Colvin <s@muelcolvin.com>

* Improve tests

* Recreate newstyle union via typing._UnionGenericAlias

* Add basic pep-604 union args order caching detection test

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Co-authored-by: ⬢ Samuel Colvin <s@muelcolvin.com>

* add test to reproduce #4949

* fix infinitely recursive deepcopy

* add test for shallow copy of wrapped dataclass

* fix infinitely recursive copy of wrapped dataclass

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Co-authored-by: Martin Billinger-Finke <2392396+mbillingr@users.noreply.github.com>

* Invalidate mypy cache if config changes

* Add docstring

* Add change description

Co-authored-by: Marc Mueller <30130371+cdce8p@users.noreply.github.com>

* Use weak refs for caches

* Fix type

* Update tests, add tests

* Update tests, add tests

* Python version check

* Improve type

* Add changes file

* Add comment

* add memray memory use test

* update deps

* use py37 generics

* move into another stage ci

* fix decorator

* fix assertion

* Remove unused LimitedDict. Add test check and comment

* Try fix memray usage

* Ignore mypy checks with memray

* tweak test setup and ci

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Co-authored-by: Adrian Garcia Badaracco <1755071+adriangb@users.noreply.github.com>
Co-authored-by: Samuel Colvin <s@muelcolvin.com>