simple-stream: Add copy constructor
simple-stream: Add copy constructor

Message-Id: <5d40b02fba53881675a9f6cec5e9fea0996b15e2@scylladb.com>

cloudius-systems/seastar,kjniemi/seastar,avikivity/seastar,cloudius-systems/seastar,dreamsxin/seastar,syuu1228/seastar,scylladb/seastar,syuu1228/seastar,avikivity/seastar,cloudius-systems/seastar,dreamsxin/seastar,scylladb/seastar,kjniemi/seastar,dreamsxin/seastar,kjniemi/seastar,syuu1228/seastar,avikivity/seastar,scylladb/seastar