Mocks::Registry::Key

Entry keys consist of two elements - the type ID and it's location in memory. For value-types, its byte-representation is stored in a pool and that location is used.

WARNING: The Class#crystal_type_id method, which is undocumented, is used to retrieve the first part of the key.

NOTE: Ideally, the type would be used as the first element of the tuple. Object.class cannot be used due to https://github.com/crystal-lang/crystal/issues/9667