Add typing to callables in transform decorators

[JimLundin]

Summary

Hello!

We are utilising foundry-dev-tools for some local development, primarily for the added type hints when using transforms.

We use the "strict=True" option for mypy type checking during our development. This setting disallows unspecified Callable types as an error when checking types. I added more specific gradual types to the "transformation_polars" and "transformation_pandas" decorators so that mypy is satisfied.

I suspect that the same type hints could be added for the pyspark transforms aswell. I can add that to this PR if that is desirable.

In the process, I also added the "Input" type to the **kwargs in the decorator signature. If required I could split that into a separate PR.

Best regards, Jim

Checklist

• [x] You agree with our CLA
• [x] Included tests (or is not applicable).
• [x] Updated documentation (or is not applicable).
• [x] Used pre-commit hooks to format and lint the code.

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[nicornk]

Hi! 👋 Thanks for the contribution. Feel free to add additional typing that you think is required (e.g. to the pyspark transform)

[JimLundin]

Added the pyspark typing to transform_df! There are more typing improvements that I think could be made to the decorators. If you would like I can continue adding to this PR or start a new one.

[nicornk]

Feel free to add further typing - let me know when you think it’s ready to be merged. Thanks!

[JimLundin]

PR looks good now! I have focused on fixing the developer-facing type hints for the transform decorators. You are welcome to merge or give feedback on the changes. When I have more time, I could help set up a github workflow for type checking and add more "internal" type hints. If that fits into the philosophy of this library.

[nicornk]

feel free to contribute additional typing PRs where you think it makes sense.