1. changes sentinel to use an http-like interface 2. moves hexutil, crypto/blake2b, metrics packages to erigon-lib
we need to extract this interface from the struct. i need to also break down the interface more, to better show what parts the caching is used, move some functions from the cache state to the underlying. don't merge
Co-authored-by: Giulio <giulio.rebuffo@gmail.com>