Keccak should compute over non-contiuous memory regions

[Scooletz]

Paprika has a copy of Keccak from Nethermind Keccak. Currently, Keccak implementation does not implement HashAlgorithm. The mentioned class provides two methods

1. HashCore(ReadOnlySpan) and
2. HashFinal()
   that can be used to construct a hash over a non-continuous memory. It'd be great if Keccak, even without implementing the actual HashAlgorithm allowed for handling the upgradability and consumption of sequences of memory.

Once provided, RLP encoding could benefit from it greatly.

Be minded, that it does not have to use ReadOnlySequence<byte> per se, but might provide some other, streaming API that could for example accept up to N spans by providing a span-like sequence or multiple overloads.

[Scooletz]

https://github.com/NethermindEth/nethermind/blob/bb5c5d5834ce631f4c611592fcb0832c6636025b/src/Nethermind/Nethermind.Core/Crypto/KeccakHash.cs#L444 Should be used.