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_f32_add/case.ww

@@ -0,0 +1,8 @@
+//ww:run-exit 10
+// Migrated from 700_e2e row 15.
+package main;
+fn add32(a: f32, b: f32) f32 = { return a + b; };
+fn main() i32 = {
+  let r: f32 = add32(2.5: f32, 7.5: f32);
+  return r: i32;
+};