Make HEP dependencies optional

[kreczko]

pip install scikit-validate should exclude HEP specific things like

• sv_root_diff
• HEP dependencies, e.g. uproot

Either have install options pip install scikit-validate[hep] or a meta-package (scikit-validate-hep) for the extra dependencies.

extras_require={
            "hep": [
                "uproot",
                  ....
            ]
        },