future: promise: mark set_value as noexcept
future: promise: mark set_value as noexcept

Now that future_state::set is noexcept.

Also, marked future_state::get_state as noexcept as it
is trivially so. It is called from promise_base_with_type::set_value.

Signed-off-by: Benny Halevy <bhalevy@scylladb.com>

Test: unit(dev)
Message-Id: <e175f1969d681e6ebd5432a17e935ac117da59ae@scylladb.com>

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