Multirange Support

[quinchs]

Summary

This PR adds the MultiRange<T> datatype as well as the backing codecs/descriptors.

[nsidnev]

Sorry if this is already there and I couldn't find it, but how this PR handles multirange for old protocol. I understand that in theory this situation just should not happen, because multirange is 4.0 feature as 2.0 protocol as well, but in python, for example, this case is taken into account and for non 2.0 version the descriptor is handled in the old way

We probably don't need it, just want to make sure it was done intentionally

[quinchs]

I didn't add it to v1 protocol since it isn't available there, I can add it if there's a case that It's available in <=v1

[nsidnev]

Well, the only way to use multirange with 1.0 is when the client explicitly requests that protocol version support from the EdgeDB 4 server. If that option doesn't exist, I think we're good here.