Improve BLS Public Key Handling

[aaronbuchwald]

When handling BLS Public Keys, we often re-verify an already verified BLS public key. However, the BLS Public Keys are verified before being added to the P-Chain, so the keys that are already part of the validator set do not need to be re-verified every time.

We should add support for handling both trusted/untrusted BLS Public Keys (may be applicable to other objects from the blst library as well) to reduce the overhead of re-verification.

Specifically, the CPU profile from the new GetValidatorSet over gRPC (#1326) shows that the majority of time is spent in CGO. This may add unnecessary overhead in both compressing the key and re-validating the key:

• https://github.com/ava-labs/avalanchego/blob/master/utils/crypto/bls/public.go#L28
• https://github.com/ava-labs/avalanchego/blob/master/utils/crypto/bls/public.go#L38

When serving these public keys over gRPC, they have already been verified, so we can treat them as trusted input and reduce the overhead here.

[hexfusion]

Another addition for this would be exposing BLS serialization/deserialization duration metrics on the client/server.