feat: easily construct function signature

[ISOR3X]

Added a construct_signature function to the Function class. This closely follows the way the jinja template works for the mkdocstrings python handler

The reason behind this PR is because I want to try to integrate python api docs into a vitepress website, but I also noticed both griffe2md and mkdocstrings/python/ have similar logic for building a function signature. Perhaps this code could replace that.

REF: #376

[ISOR3X]

Those errors do not seem to come from my code so I am not sure what to do. This is one of my first time contributing to open sources projects to I might need some guidance here.

[pawamoy]

Thanks a lot for your PR @ISOR3X!

The errors I see in the CI logs do seem to come from your changes: you removed the Union import in src/_griffe/models.py and Ruff is complaining.

You also added spacing changes that are irrelevant to the feature here (added tabulations), could you revert these? You can run make format to format the code according to the project rules.

[ISOR3X]

Fixed the formatting but the CI still seems to fail...

Also make format doesn't work for me, but I did noticed my IDE (PyCharm) automatically made a venv when opening the project, do you know something about this?

[ISOR3X]

I was worried that this was forgotten, glad to see it's not!

[pawamoy]

LGTM, thanks a lot!