Remove the serialization logic from the storage layer

[robert-zaremba]

Summary

It seams that IAVL is responsible for both specific data serialization and the storage mechanism. This creates a tight coupling between the logic layer and storage layer. As a general principle, storage shouldn't depend on the data serialization required by the upper layers.

Problem Definition

Any future changes on state commitment layer will impact re-implementation of the serialization layer. It's only the

Proposal

Move the serialization layer out of the IAVL and enable clear interface between the layers: app, storage driver, storage engine.

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[alexanderbez]

Given that IAVL stores are logical stores, where do you see the serialization? The IAVL KVStore doesn't serialize anything -- it works on raw bytes.

[robert-zaremba]

This is what I've got when discussing with @amaurymartiny on #6194
@clevinson

[amaury1093]

That was the impression I got when reading issues like cosmos/iavl#242. But I also started looking into IAVL code ~10 days ago, so am definitely lacking big picture context for IAVL. Sorry if I misled someone into wrong directions.

[robert-zaremba]

Shall we close this issue?

[alexanderbez]

Seems like this should be moved to the IAVL repo then? I don't see what the SDK has to do with anything here.