Use type aliasing or embedded types for handling protobuf and ed25519 operations

[robert-zaremba]

Summary

Signatures are heavily used blockchain workload, so if possible it's good to avoid unnecessary conversion operations

Problem Definition

In #7268 we introduce back ed25519 in SDK. The first implementation makes conversion to x/crypto/ed25519 each time we call any signature related function. This is suboptimal.

Ref: https://github.com/cosmos/cosmos-sdk/pull/7268/files#r493581731

Proposal

We can experiment with type alias or embed stdlib crypto/ed25519 PubKey and PrivateKey. This approach will remove type conversions and unnecessary memory allocations, but we will still need to keep method wrappers.

gogoproto.casttype can be used to instrument protobuf compiler.

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[robert-zaremba]

Solved in: #7672