M13.27: sim effects golden hashes

Pin exact CPU pixel hashes of the simulation effects refactored into shared
GPU plans in M13.23 (CC Rainfall/Snowfall/Star Burst/Bubbles/Drizzle/Hair/
Mr. Mercury, Caustics, Wave World, Foam, Shatter, Card Dance, Card Wipe):
404 frames over default and non-default settings, four times incl. a seek
backwards, 8 and 32 bpc, full and half resolution. Verified bit-identical
between 7a5a93b (before M13.23) and 808ca70 (after).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/testing.md

@@ -16,7 +16,10 @@ cargo xtask ci             # fmt, clippy -D warnings, tests, layers, assets, was
 - **Effects** (`crates/effects`): each effect has a determinism test and at least one behaviour
   test (identity at neutral settings, known pixel results, or simulations giving the same frame
   whether you seek straight to it or play up to it). A registry-wide test checks that effects
-  which read the clock are declared time-dependent.
+  which read the clock are declared time-dependent. `crates/effects/tests/sim_golden.rs` pins
+  exact pixel hashes of the simulation effects the GPU shares plans with (CC Rainfall … Card
+  Wipe) at several settings, times, bit depths and resolutions, so any change to their CPU output
+  fails (re-pin with `SIM_GOLDEN_PRINT=1` after an intended change; pinned for aarch64 macOS).
 - **Export** (`crates/export/tests`): every format is encoded and decoded back, checking frame
   count, size and pixels. When `ffmpeg`/`ffprobe` are installed they are used as an outside
   check; they are never linked or shipped.