Revive test_compute_kzg_proof_within_domain() -- but not exhaustive

It now creates 6 random proofs instead of all 4096.

tests/core/pyspec/eth2spec/test/deneb/unittests/polynomial_commitments/test_polynomial_commitments.py

@@ -167,6 +167,28 @@ def test_barycentric_within_domain(spec):
         assert p_z_coeff == p_z_eval == poly_eval[i]
 
 
+@with_deneb_and_later
+@spec_test
+@single_phase
+def test_compute_kzg_proof_within_domain(spec):
+    """
+    Create and verify KZG proof that p(z) == y
+    where z is in the domain of our KZG scheme (i.e. a relevant root of unity).
+    """
+    rng = random.Random(5566)
+    blob = get_sample_blob(spec)
+    commitment = spec.blob_to_kzg_commitment(blob)
+    polynomial = spec.blob_to_polynomial(blob)
+
+    roots_of_unity_brp = spec.bit_reversal_permutation(spec.ROOTS_OF_UNITY)
+
+    # Let's test some roots of unity
+    for _ in range(6):
+        z = rng.choice(roots_of_unity_brp)
+        proof, y = spec.compute_kzg_proof_impl(polynomial, z)
+        assert spec.verify_kzg_proof_impl(commitment, z, y, proof)
+
+
 @with_deneb_and_later
 @spec_test
 @single_phase