cql3: prepare_context: mark methods noexcept
cql3: prepare_context: mark methods noexcept

Prepare for marking deferred actions noexcept.

Signed-off-by: Benny Halevy <23c997c90eb8537635e9392d48e7af1bf1b2ca22@scylladb.com>

scylladb/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla