sds: support converting bloom filter between bytes and arrays of bigint

[adklempner]

The BloomFilter class stores its bit vectors as an array of bigint. When serializing into a SDS message, it needs to be byte-encoded. When receiving SDS messages, it needs to be decoded from bytes back to an array of bigint in order to run lookup operations.

The method for encoding and decoding must be interoperable with the nim implementation. e.g. if A (running SDS in browser) and B (running SDS in a nim service) both insert the same set of message IDs into the filter and attach it to a message sent to the other party, both must get positive results when looking up those message IDs in the attached bloom filters.

nim implementation for reference: https://github.com/waku-org/nim-sds/blob/89160b58d4929691df95296f15d8eaad8c50f1dc/src/protobuf.nim#L59