Implements Struct_builder concept with maximal zero-copy perf by (1) storing the actual user-schema-c...">shm::Builder</a>; but <a class="el" href="classipc_1_1transport_1_1struc_1_1shm_1_1Capnp__message__builder.html" title="A capnp::MessageBuilder used by shm::Builder: similar to a MallocMessageBuilder with the GROW_HEURIST...">Capnp_message_builder</a> is also usable as a <code>capnp::MessageBuilder</code> directly. If a user were to indeed leverage it in that latter capacity, they may want to transmit/s