Add support for generic TypeProxies for all SGQLC types

[n-wach]

@senormeow pointed out that we can use TypeProxy for classes that aren't specifically subclassed. This can be used to TypeProxy all SGQLC types so the same methods (like to_json) exist on all types and the user has to worry about proxying even less.

• Set underlying_type in __init__
• Update attr proxying logic to return generic TypeProxy if type isn't scalar and doesn't have known TypeProxy subclass
• Move proxying up to the ConservatorConnection.query level (we are aware of type at this point, shouldn't make caller proxy themselves)