Merge bitcoin#30372: util: Use SteadyClock in RandAddSeedPerfmon

fa360b0 util: Use SteadyClock in RandAddSeedPerfmon (MarcoFalke)

Pull request description:

  `GetTime` is mockable in tests and system-changeable in production. This should be fine and not lead to issues, but using `SteadyClock` is more correct in this context to do an expensive task only so often.

ACKs for top commit:
  sipa:
    utACK fa360b0
  TheCharlatan:
    ACK fa360b0

Tree-SHA512: 1958b9e9e356c9801ac981014b4b528cfc8ce6612853d8b45f6519b16f0b1839ff765abb8b3368b86f00958ddc6a686f6b90278c57a7ad4858bdf3ea33775cca

src/randomenv.cpp

@@ -69,10 +69,10 @@ void RandAddSeedPerfmon(CSHA512& hasher)
 
     // This can take up to 2 seconds, so only do it every 10 minutes.
     // Initialize last_perfmon to 0 seconds, we don't skip the first call.
-    static std::atomic<std::chrono::seconds> last_perfmon{0s};
+    static std::atomic<SteadyClock::time_point> last_perfmon{SteadyClock::time_point{0s}};
     auto last_time = last_perfmon.load();
-    auto current_time = GetTime<std::chrono::seconds>();
-    if (current_time < last_time + std::chrono::minutes{10}) return;
+    auto current_time = SteadyClock::now();
+    if (current_time < last_time + 10min) return;
     last_perfmon = current_time;
 
     std::vector<unsigned char> vData(250000, 0);