Proposing add_formal_parameter function

[LauLauThom]

Following yesterday's call, here is a small PR proposing the addition of a function to facilitate the definition of FormalParameters in a workflow crate.

It makes use of type hints, which is available from python 3.5, support could be added for earlier version by adding the typing package to the list of dependencies, checking the version of python to only install if needed.

I am happy to write tests and documentation for this function if you think that's a valid addition.
Currently it can be tested with

from rocrate.rocrate import ROCrate
from pprint import pprint

crate = ROCrate()
formal_parameter = crate.add_formal_parameter(identifier = "my_param",
                                              additionalType = "Text",
                                              name = "my_param",
                                              description = "",
                                              valueRequired = False,
                                              defaultValue = "")
pprint(formal_parameter.as_jsonld())

Actually for testing I typically install the package in editable mode like so
pip install -e .
but I got an exception that it's not possible

DEPRECATION: Legacy editable install of rocrate==0.13.0 from file:///Users/thomasl/Documents/repos/ro-crate-py (setup.py develop) is deprecated. pip 25.1 will enforce this behaviour change. A possible replacement is to add a pyproject.toml or enable --use-pep517, and use setuptools >= 64. If the resulting installation is not behaving as expected, try using --config-settings editable_mode=compat. Please consult the setuptools documentation for more information. Discussion can be found at https://github.com/pypa/pip/issues/11457

So I was wondering how you test it usually.
I also had issues with test discovery, but that's maybe something with my VScode config.

Cheers !