[runtime_stats] Track main loop active time and report overhead (#15743)

esphome/core/component.cpp

@@ -506,6 +506,10 @@ void PollingComponent::stop_poller() {
 
 uint32_t PollingComponent::get_update_interval() const { return this->update_interval_; }
 
+#ifdef USE_RUNTIME_STATS
+uint64_t ComponentRuntimeStats::global_recorded_us = 0;  // NOLINT(cppcoreguidelines-avoid-non-const-global-variables)
+#endif
+
 void __attribute__((noinline, cold))
 WarnIfComponentBlockingGuard::warn_blocking(Component *component, uint32_t blocking_time) {
   bool should_warn;