WIP: class based api

[slavikovbasa]

Added type conversions (built-ins -> hiku types), as the first step of class-based API implementation.

For now covering built-in scalars (int, float, bool, str) + containers (list, optional) + typerefs for custom object types. With the refs to python classes cyclic imports become a real problem, so I added lazy annotation for that purpose (influenced by strawberry). I was not too concerned about python versioning so far - I will use proper typing_extension imports and so on after the basic stuff is ready and working.

My main concern is being able to gradually update existing definitions with class-based API - for that purpose raw_type annotation was added. Basically raw_type could be all we need to start writing classes, though typing.Annotated stuff does look cumbersome - that's why I decided to cover some basic cases (scalars, containers, typerefs) too. Interfaces, unions, enums, custom scalars (including hiku.types.ID and hiku.types.Any) for now require the use of raw_type. Later there should be no problems implementing interfaces via class inheritance, unions and custom scalars via type aliases, enums - using enum stdlib.

For the next step, I plan to add transformations of class-based nodes to hiku.graph.Node. I believe, that it should go to Graph.__init__: lazy imports should be able to resolve just fine there (cuz all nodes have to be imported anyway to be passed to Graph.items). During transformation I plan to auto-transform field names to camelCase and add some default resolvers, all other params unchanged for now.

[slavikovbasa]

I am open to the discussion on everything - naming, algorithms, ideas and so on

[kindermax]

Overall this looks like a good starting point. Lets go with this and see where it goes.