route namespace

design notes for #850

I estimate completing the implementation will take half a day.


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UPDATE (from Adam): This took over a day to change it from design to implementation, including hours of pairing, but the estimate was for Jean-Paul alone and I'm slower. There are also a few TODOs with questions about how to continue.

Fixes #850 

`namespace` attribute is not part of `INetwork`... so either tests and code shouldn't rely on it, or you should add it to `INetwork`. It's not clear to me it's a useful part of the interface, and so I would say tests and external users shouldn't rely on it.

If no one relies on it then you dont have to have a default here. And memory network doesn't have to have anything at all related to namespaces.