Revise all uses of metadata to see if named metadata should be used

[addisoncrump]

We use normal metadata in several places where named metadata should be used (e.g., you cannot have multiple MOpt instances with a single state). We should revise everywhere that we use metadata to see if named metadata should be used instead.

[domenukk]

One issue is that named has extra overhead over non-named, right? Since it's two hash lookups instead of one

[addisoncrump]

Perhaps so, but as it stands it is outright wrong. We'll need to document compatibilities if nothing else.