[Zephyr] Save total operational hours on Read

Currently total operational hours are saved to NVM with
`CONFIG_CHIP_OPERATIONAL_TIME_SAVE_INTERVAL`.
Certification tests require checking the value after 1 hour,
restarting the DUT, and checking if the value has not changed,
causing failures if given config is higher than 1.

This commit additionaly saves total operational hours to NVM
everytime it is being read by `GetTotalOperationalHours`
(writing only if currently stored value should be updated).
This way value is stored with minimum frequency of 1 hour (if
read request is sent frequently) and maximum frequency of
`CONFIG_CHIP_OPERATIONAL_TIME_SAVE_INTERVAL`.

src/platform/Zephyr/DiagnosticDataProviderImpl.cpp

@@ -282,6 +282,11 @@ CHIP_ERROR DiagnosticDataProviderImpl::GetTotalOperationalHours(uint32_t & total
 
     totalOperationalHours = static_cast<uint32_t>(totalHours + deltaTime < UINT32_MAX ? totalHours + deltaTime : UINT32_MAX);
 
+    if (deltaTime > 0) {
+        ReturnErrorOnFailure(ConfigurationMgr().StoreTotalOperationalHours(totalOperationalHours));
+        PlatformMgrImpl().SetSavedOperationalHoursSinceBoot(upTimeH);
+    }
+
     return CHIP_NO_ERROR;
 }
 

src/platform/Zephyr/PlatformManagerImpl.h

@@ -48,6 +48,7 @@ class PlatformManagerImpl final : public PlatformManager, public Internal::Gener
 
     System::Clock::Timestamp GetStartTime() { return mStartTime; }
     uint32_t GetSavedOperationalHoursSinceBoot() { return mSavedOperationalHoursSinceBoot; }
+    void SetSavedOperationalHoursSinceBoot(uint32_t hours) { mSavedOperationalHoursSinceBoot = hours; }
 
 private:
     // ===== Methods that implement the PlatformManager abstract interface.