remove dependency from `pkg_resources`

we get a warning when running `mavisp`:

```
/data/user/teo/devel/MAVISp/mavisp/modules.py:28: UserWarning: pkg_resources is deprecated as an API. See https://setuptools.pypa.io/en/latest/pkg_resources.html. The pkg_resources package is slated for removal as early as 2025-11-30. Refrain from using this package or pin to Setuptools<81.
```