Restrict vectorized systems to always have "norbs" defined
I haven't checked in the relevant places in the code to see if we already do this, but I noticed in the docs for system.VectorizedSystem
the following note about site_ranges
:
``None`` if any site array
in 'site_arrays' does not have 'norbs' specified. Note 'site_ranges'
is directly computable from 'site_arrays'.
IMO we should require users to specify norbs
if they are using the vectorized interface (because they will have to upgrade their scripts anyway). This will make implementation simpler because we can assume that if something is a vectorized system then it has norbs specified, which is often useful.