Add ICARUSCVN module to icaruscode

[fwieler]

This PR adds the ICARUSCVN module to the icaruscode repository.

ICARUSCVN is a convolutional visual (neural) network (CVN) module designed to analyze ICARUS detector events. It classifies neutrino interactions by flavor.

Changes Include:

1. fcls/ – FHiCL configuration files and scripts for evaluation and mapping
2. module_helpers/ – helper classes, utilities, and interfaces
3. modules/ – ART modules: ICARUSCVNEvaluator, ICARUSCVNMapper, ICARUSCVNZlibMaker, ICARUSTFNetHandler_tool
4. tf/ – TensorFlow graph interface and related code
5. Updated icaruscode/CMakeLists.txt to include the ICARUSCVN module
6. Added .gitignore in ICARUSCVN to ignore trained AI model files

Some studies related to the icaruscvn can be found here:
SBN DocDB 43786
SBN DocDB 44104

[jas1005]

@acampani, @brucehoward-physics, and @cerati

I'm going through old PRs and it looks like this one never got approved. I realize the number of changes is quite large, but I hope your relative familiarity with the code will make things easier. Do y'all have time to review this PR or should I ask someone else?