better error handling for managed site installations

[mbway]

With MaturinBuildSettings and MaturinDevelopSettings removed in #11 I was concerned about what would happen if users are importing these classes in sitecustomize.py. Looking at the 0.1.0 release, the presets option wasn't available so it's unlikely many user's installs will break.

It seems that when something breaks in sitecustomize.py an error is printed but the interpreter continues. To help the user resolve the problem, managed installations now print a message informing the user how they can remove the installation to resolve the error:

$ python
Error in sitecustomize; set PYTHONVERBOSE for traceback:
RuntimeError: MaturinSettings.__init__() got an unexpected keyword argument 'asdf'
>> ERROR in managed maturin_import_hook installation. Remove with `python -m maturin_import_hook site uninstall`

Python 3.13.1 (main, Dec  6 2024, 18:40:43) [Clang 18.1.8 ] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> 

In future, if any maturin flags change and MaturinSettings changes to match, breakages could become more common so it is important to handle this case properly.