ffi 1.32 backfill: locked-in test for #objc_call(CGRect) + #objc_call(u64)

Closes the runtime-verification gap from cluster 1.32. The migrated
`uikit_keyboard_will_change_frame` body uses both shapes but isn't
reached by chess startup (the soft keyboard doesn't open without user
input), so runtime verification was transitive only: `#objc_call(CGRect)`
via the structurally-identical `#objc_call(UIEdgeInsets)` (4×f64 HFA)
in ffi-objc-call-07, and `#objc_call(u64)` via the LLVM-equivalent
`#objc_call(s64)` `hash` test in ffi-objc-call-04.

This example installs two IMPs via `class_addMethod`:
- `rect_imp` returns a CGRect of {10.5, 20.5, 30.5, 40.5} through the
  32-byte HFA path (v0..v3 on AAPCS64).
- `u64_imp` returns `0x7FEDCBA987654321` through the i64 path.

`#objc_call(CGRect)` and `#objc_call(u64)` dispatch through them and
the values are printed for snapshot lockdown.

Reused the parser quirk noted in the checkpoint and in 0.1 — integer
literals ≥ 2^63 are rejected even when the receiving type is u64, so
the test value keeps the high bit clear.

111/111 host tests pass.

tests/expected/ffi-objc-call-12-rect-u64-returns.exit

@@ -0,0 +1 @@
+0

tests/expected/ffi-objc-call-12-rect-u64-returns.txt

@@ -0,0 +1,2 @@
+rect = (10.500000, 20.500000, 30.500000, 40.500000)
+uval = 9218247941278745377