test: migrate 700_e2e rows to corpus fixtures; retire the carrier

136 rows migrated, 0 already owned, 3 wwstage-failing rows held out.

test/wcc/data/r700_defer_implicit_ret/case.ww

@@ -0,0 +1,17 @@
+//ww:run-exit 87
+// Migrated from 700_e2e row 63.
+package main;
+fn rec(p: *i32, c: i32) i32 = {
+  *p = *p * 10 + c;
+  return 0;
+};
+fn run(p: *i32) void = {
+  defer rec(p, 7);
+  defer rec(p, 8);
+  // no explicit return — implicit fall-through path
+};
+fn main() i32 = {
+  let acc: i32 = 0;
+  run(&acc);
+  return acc;
+};