Schema storage and reference lookup

[Strech]

:avro_schema_store has a few limitations, you can't delete or update schemas there. Avro.Storage.Memory is used like a cache for schema resolution, but it's used only by the Avrora.Resolver.

The issue occurs when we try to resolve a schema with references. First of all, it's different per storage, Avrora.Storage.File will read only the content of the referenced schemas and never "cache" them. Avrora.Storage.Registry on the other hand going to create new Avrora.Schema objects, but use only JSON and pass it to the reference resolver which will parse it again. None of the referenced objects will be "cached".

It feels like we need to be able to resolve references smartly without repetitive calls to the disk or registry API.