fix: data.atomic_mass accept str parameter
fix: data.atomic_mass accept str parameter

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