Add more NuGraph2 variables to CAFs

[rtriozzi]

This PR adds some plane-by-plane slice-level variables to the CAFs, based on the predictions from NuGraph2.
Specifically:

• the number of hits tagged by NuGraph2 for each category in the slice (e.g., shr_hits for the Shower category);
• ng_vtx_hip_hits: the number of "HIP" hits tagged by NuGraph2 near the reconstructed interaction vertex. Wire and tick allowed distances are configurable. Standard is 10 wires and 50 ticks;
• unclustered_shr_hits: the number of hits tagged as "shower" by NuGraph2 in the slice, that are not associated to any reconstructed PFP.

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Associated PRs

• Handle CAF making when Pandora runs after the NuGraph2 filter sbncode#616

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Checklist

• Have you run git fetch and pulled the latest changes from the branch you're basing your PR against? Will do, after review.
• If you're adding new classes, have you added them to classes_def.xml in the relevant directory?
• Have you added a checksum in classes_def.xml to any and all new classes you're implementing, and rebuilt?
• If you're updating classes, have you incremented the ClassVersion by one compared to develop in classes_def.xml?

[cerati]

Looks great to me, thanks!