wscript: memory and faults

Pure reference counting (cycles leak; break with weak); VM faults are trappable host errors with a stack trace.

Memory is pure reference counting — cycles leak (no cycle collector); break cycles with weak(x) / w.upgrade() -> Option[T].

VM faults (index OOB, divide by zero, unwrap() on None) are trappable errors delivered to the host with a stack trace — in config-weave they surface as the step's Error status. Prefer xs.get(i) / m.get(k) where failure is expected.