add Containers_bencode for lightweight (de)ser

perf(CCHash): improve a bit commutative hashing of arrays/lists

perf(CCHash): only hash prefix of string/bytes

feat(CCList): Add Assoc.{keys,values,map_values}

feat(CCArray): add CCArray.map_inplace

add CCString.{to_hex,of_hex}

fix(Atomic): prevent race conditions under flambda, for now