test: port 732_def_const_fold residue to corpus fixtures

732_def_const_fold.c -> r732_def_xmod_fold (run-exit 42; stronger than
  the carrier's DATA-row grep — links AND reads the folded cross-module
  value), r732_def_xmod_cycle (error 'def value: reference chain too
  deep', upgrading the needle-less exit!=0 check).

The five same-module exec rows and both same-module fail-loud rows were
already owned by the r732_def_* fixtures; their cs-vs-ww byte identity
rides test-data-byteid, which now also covers the xmod fold row. The
timeout-124 hang distinction devolves to the wwfixture harness timeout.

test/wcc/data/r732_def_xmod_cycle/case.ww

@@ -0,0 +1,9 @@
+//ww:error "def value: reference chain too deep"
+// migrated from test/wcc/732_def_const_fold.c: cross-module def cycle (a.J -> b.K -> a.J) must fail loud, not hang or emit silently.
+package a;
+import b;
+export def J: i32 = b.K;
+package b;
+import a;
+export def K: i32 = a.J;
+export fn main() i32 = { return 0; };