optimize serialization of array/vector of integral types
optimize serialization of array/vector of integral types

Array of integral types on little endian machine can be memcpyed into/out
of a buffer instead of serialized/deserialized element by element.

Message-Id: <e3c698c615594272003709911e4f2ddcf7806532@scylladb.com>

duarten/scylla,avikivity/scylla,raphaelsc/scylla,scylladb/scylla,avikivity/scylla,kjniemi/scylla,scylladb/scylla,duarten/scylla,raphaelsc/scylla,kjniemi/scylla,scylladb/scylla,duarten/scylla,kjniemi/scylla,raphaelsc/scylla,scylladb/scylla,avikivity/scylla