Measure APCER with a dedicated spoof dataset (CelebA-Spoof)

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**Location:** `fivucsas-test/04_liveness_spoofing/test_liveness_spoofing.py:235`

```
TODO: Download CelebA-Spoof and re-run to measure APCER
```

The marker stays in the code (annotated `(#this)` in place).

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_Migrated from `fivucsas-test/04_liveness_spoofing/test_liveness_spoofing.py:235`._