Class cache

[diamondburned]

In order to implement a collision-free method inheritance system in gotk4, a class/interface cache is required, because resolving a tree repeatedly and recursively for every single method is simply not feasible and will blow up generation time to minutes.

The cache would likely have to:

• work at the generation level inside iface.Generator
• be integrated with the Generator interface to make it not leaky

All code using methods should also rely on the iface.Generator, especially when caching it makes it very cheap to do so.

[diamondburned]

For now, methods will simply not be carried over.