[uptime] Use scheduler millis_64() for rollover-safe uptime tracking (#14170)

esphome/core/scheduler.cpp

@@ -675,6 +675,8 @@ bool HOT Scheduler::cancel_item_locked_(Component *component, NameType name_type
   return total_cancelled > 0;
 }
 
+uint64_t Scheduler::millis_64() { return this->millis_64_(millis()); }
+
 uint64_t Scheduler::millis_64_(uint32_t now) {
   // THREAD SAFETY NOTE:
   // This function has three implementations, based on the precompiler flags