Created _CrossNuclide private class for tally arithmetic
Created _CrossNuclide private class for tally arithmetic

walshjon/openmc,smharper/openmc,smharper/openmc,smharper/openmc,wbinventor/openmc,samuelshaner/openmc,johnnyliu27/openmc,paulromano/openmc,amandalund/openmc,bhermanmit/openmc,amandalund/openmc,mit-crpg/openmc,wbinventor/openmc,paulromano/openmc,bhermanmit/openmc,liangjg/openmc,mjlong/openmc,kellyrowland/openmc,shikhar413/openmc,samuelshaner/openmc,shikhar413/openmc,amandalund/openmc,mit-crpg/openmc,johnnyliu27/openmc,wbinventor/openmc,johnnyliu27/openmc,kellyrowland/openmc,walshjon/openmc,walshjon/openmc,liangjg/openmc,paulromano/openmc,johnnyliu27/openmc,mit-crpg/openmc,amandalund/openmc,mjlong/openmc,liangjg/openmc,smharper/openmc,shikhar413/openmc,mit-crpg/openmc,paulromano/openmc,samuelshaner/openmc,samuelshaner/openmc,shikhar413/openmc,wbinventor/openmc,liangjg/openmc,walshjon/openmc