[CI] Test federated learning plugin in the CI (#8325)

tests/cpp/plugin/helpers.cc

@@ -0,0 +1,19 @@
+#include <chrono>
+#include <thread>
+#include <random>
+#include <cstdint>
+
+#include "helpers.h"
+
+using namespace std::chrono_literals;
+
+int GenerateRandomPort(int low, int high) {
+  // Ensure unique timestamp by introducing a small artificial delay
+  std::this_thread::sleep_for(100ms);
+  auto timestamp = static_cast<uint64_t>(std::chrono::duration_cast<std::chrono::milliseconds>(
+    std::chrono::system_clock::now().time_since_epoch()).count());
+  std::mt19937_64 rng(timestamp);
+  std::uniform_int_distribution<int> dist(low, high);
+  int port = dist(rng);
+  return port;
+}