On further thought using an interner here doesn't make much sense (can't do fast equality check; only identity, simple types are as big as the Ref, no plans of incremental compilation). I'm going to instead look into using tagged pointers which also enable variable size and different storage/unwrapped representation.

I'm not very familiar with the clang codebase but I was curious how they handle types and it sounds like they might do something similar (with tagged pointers) https://github.com/llvm/llvm-project/blob/ce731770f869e8e61afa2dccb772e8367105a1a6/clang/include/clang/AST/Type.h#L740