Implement pre/post processing convenience functions for e.g. `MessageCache`

An example is converting the dimension names of a cache of messages to match that of the norm network:

function validate_message(nn::NormNetwork, message)
    return if !any(name -> has_dimname(KetView(nn), name), dimnames(message))
        error(
            "provided message does not have have any index \
            names in common with the tensor network contained in the norm."
        )
    end
end

function stateform(nn::NormNetwork, messages)
    renamed_messages = map(messages) do msg
        if !any(name -> has_dimname(KetView(nn), name), dimnames(msg))
            error(
                "provided message does not have have any index \
                names in common with the tensor network contained in the norm."
            )
        end

        bramap = Dict(codomainnames(msg) .=> Base.Fix1(braname, nn).(domainnames(msg)))

        return replacedimnames(name -> get(bramap, name, name), state(msg))
    end
    return MessageCache(renamed_messages)
end

function operatorform(nn::NormNetwork, messages)
    return messagecache(keys(messages)) do edge

        validate_message(nn, messages[edge])

        ketnames = linknames(KetView(nn), edge)
        branames = linknames(BraView(nn), edge)

        bramap = Dict(branames .=> Base.Fix1(braname, nn).(ketnames))

        renamed_message = replacedimnames(name -> get(bramap, name, name), messages[edge])

        return operator(renamed_message, branames, ketnames)
    end
end

Originally posted by @jack-dunham in https://github.com/ITensor/ITensorNetworksNext.jl/pull/119#discussion_r3494007113

Start by locating the MessageCache and NormNetwork APIs, then compare their existing message and dimension-name handling with the validate_message, stateform, and operatorform examples in this issue. Define the convenience-function entry points and verify that they perform the shown validation, renaming, and operator conversion behavior for cached messages.