Replace deprecated imp by importlib

[fredroy]

https://docs.python.org/dev/whatsnew/3.12.html#imp

Imp has been deprecated since Python3 3.4 (!) and has been removed in 3.12.1 Hitting first macOS users because homebrew recently updated their version.

More context : https://discuss.python.org/t/how-do-i-migrate-from-imp/27885/13

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livecoding.py is called in PythonEnvironment, so it is throwing an error every time.

This PR replaces imp by importlib.

I just tested by calling directly the file (and using the onReimpAFile(file). There is no test at all currently and this onReimpAFile() function is only used for prefab.

Fix partially https://github.com/sofa-framework/sofa/discussions/4624

[adagolodjo]

@damienmarchal, @olivier-roussel, @hugtalbot can we merge this ? Thanks.

[damienmarchal]

Yes