feat: add several scikit-hep python packages

This PR adds a few scikit-hep python packages to ensure that they are pre-installed and available for benchmarks (without pulling them in when the requirements.txt is called).

hepunits~=2.3.2
hist~=2.6.1
histoprint~=2.4.0
particle~=0.23.0
vector~=0.8.5

Note: The version of vector will be updated to the latest 1.4.0, but that will take a bit longer.

spack-environment/packages.yaml

@@ -278,7 +278,7 @@ packages:
     - '@2.3.4'
   py-hist:
     require:
-    - '@2.7.3'
+    - '@2.6.1'
   py-histoprint:
     require:
     - '@2.4.0'