bench: make EvictionProtection.* work with any number of iterations

Moves copying of the setup into the benchmark loop so it is possible
to run the loop for an arbitrary number of times.

The overhead due to copying the candidates inside the loop is about 3%.

src/bench/peer_eviction.cpp

@@ -20,19 +20,17 @@ static void EvictionProtectionCommon(
 {
     using Candidates = std::vector<NodeEvictionCandidate>;
     FastRandomContext random_context{true};
-    bench.warmup(100).epochIterations(1100);
 
     Candidates candidates{GetRandomNodeEvictionCandidates(num_candidates, random_context)};
     for (auto& c : candidates) {
         candidate_setup_fn(c);
     }
 
-    std::vector<Candidates> copies{
-        static_cast<size_t>(bench.epochs() * bench.epochIterations()), candidates};
-    size_t i{0};
+
     bench.run([&] {
-        ProtectEvictionCandidatesByRatio(copies.at(i));
-        ++i;
+        // creating a copy has an overhead of about 3%, so it does not influence the benchmark results much.
+        auto copy = candidates;
+        ProtectEvictionCandidatesByRatio(copy);
     });
 }