Make ML-DSA Sign Benchmarking Deterministic

[itzmeanjan]

When benchmarking ML-DSA sign function, we random sample all input arguments, making the algorithm non-deterministic - resulting in variable timing. This doesn't give correct performance profile during benchmarking.

ml-dsa/benchmarks/bench_ml_dsa_44.cpp

Lines 29 to 68 in 5e24387

	// Benchmark performance of ML-DSA-44 signing algorithm.
	void
	ml_dsa_44_sign(benchmark::State& state)
	{
	const size_t mlen = state.range(0);
	std::vector<uint8_t> msg(mlen, 0);
	auto msg_span = std::span(msg);
	std::array<uint8_t, ml_dsa_44::KeygenSeedByteLen> seed{};
	std::array<uint8_t, ml_dsa_44::PubKeyByteLen> pubkey{};
	std::array<uint8_t, ml_dsa_44::SecKeyByteLen> seckey{};
	std::array<uint8_t, ml_dsa_44::SigningSeedByteLen> rnd{};
	std::array<uint8_t, ml_dsa_44::SigByteLen> sig{};
	randomshake::randomshake_t<128> csprng;
	csprng.generate(seed);
	csprng.generate(rnd);
	csprng.generate(msg_span);
	ml_dsa_44::keygen(seed, pubkey, seckey);
	bool has_signed = true;
	for (auto _ : state) {
	benchmark::DoNotOptimize(has_signed);
	benchmark::DoNotOptimize(rnd);
	benchmark::DoNotOptimize(seckey);
	benchmark::DoNotOptimize(msg_span);
	benchmark::DoNotOptimize(sig);
	has_signed &= ml_dsa_44::sign(rnd, seckey, msg_span, {}, sig);
	benchmark::ClobberMemory();
	}
	assert(has_signed);
	assert(ml_dsa_44::verify(pubkey, msg_span, {}, sig));
	state.SetItemsProcessed(state.iterations());
	}

To avoid this, we can seed the RandomShake CSRPNG (cryptographically secure pseudo-random number generator) with a fixed seed. Address it and update benchmark results. This will also make it easy to spot any performance degradation or optimization.