Add to nqp/t/serialization/01-basic.t run_tests.
add a compose method to P6int repr
set the type check cache in KnowHOW
Pass nqp/t/serialization/02-types.t.

Implement nqp::scsetcode, nqp::markcodestatic.
Do more thing inside P6opaque REPR .compose.
Mark the contents of the 6MODEL_CORE sc as coming from that sc.