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/r800append_struct_call_gp16/case.ww

@@ -0,0 +1,16 @@
+//ww:run-exit 0
+// Graduated #34 reject pin: a 16B GP struct CALL element appends
+// through the per-site scratch receive (was the loudstop fixture).
+package main;
+type pt = struct { x: i32, y: i32, z: i64 };
+fn mk() pt = {
+	return pt { x = 1, y = 2, z = 3 };
+};
+export fn main() i32 = {
+	let xs: []pt = [];
+	append(xs, mk());
+	if (xs.len != 1) { return 1; };
+	if (xs[0].x != 1 || xs[0].y != 2) { return 2; };
+	if (xs[0].z != 3i64) { return 3; };
+	return 0;
+};