Fix CI (plus DX improvements)

[evenicoulddoit]

What does this change

• Uses extras_require to enforce consistent versioning of development / ci / testing requirements
• Bumps mypy to latest version supported by Python 3.8
• Updates CI to use tox to run mypy

What was wrong

• The @overload decorator wasn't supported across the repo, due to the lack of support in the stub file generation
• This prevented proper typing support for users who were trying to use the faker library
• The development experience with Faker was made more difficult due to development and test requirements not being formalized centrally

How this fixes it

• Addresses all of the above

Notes

• This is a pre-requisite for Fix typing for uuid4() #2164

Checklist

• I have read the documentation about CONTRIBUTING
• I have read the documentation about Coding style
• I have run make lint

[evenicoulddoit]

@fcurella MyPy is failing, but it's running against the latest version as CI is governed by the state of the master branch. Having copied the process via my fork, you can see that these changes will pass CI once fixed: https://github.com/evenicoulddoit/faker/actions/runs/13195989491/job/36837366554?pr=4

[fcurella]

Can you please undo all the DX changes, so we can review them in a separate PR?

[evenicoulddoit]

@fcurella yes and no. The crucial fix here I think is bumping MyPy. This isn't fixed on the master branch. This PR applies strict limits across the board, and uses them. I can produce a PR which just bumps MyPy but it would also fail for the reasons above?