Add cnpy to spack

cnpy: library for writing npy files from c/c++

spack.yaml

@@ -4,6 +4,7 @@ spack:
     - cairo@1.16.0 +fc+ft+X+pdf+gobject
     - clhep@2.4.4.0 cxxstd=17
     - cmake@3.21.4
+    - cnpy@master
     - dawn@3_91a
     - dawncut@1_54a
     - dd4hep@1.20.1 +geant4 -assimp +hepmc3 +ipo +lcio