[main] Protocol changes to simplify bridging

[deuszx]

While working on the bridge compatible with testnet conway, some suboptimal design decisions had to be made to make it work for the protocol compatible with testnet conway. When developing for main (and next testnet release) we can change the protocol to simplify:

1. Validator secp256k1 keys (verifying/protocol keys, not accounts) are in compressed form. This makes the signature verification more costly on the EVM. We should post uncompressed keys and simplify verification.