[Follow-up] Ensure only complete block utilisation data is considered

This ticket was created to fix bug #5168 . As an interim measure, discovery/analysis of the issue was completed via #5168 , including the interim step to add the logging for future reference.

This ticket will be used to fix the bug. The background from #5168 is;

> Background:
>
> [@zajko](https://github.com/zajko) suspected a bug where a node that missed blocks due to disconnection could miscalculate utilisation and incorrectly determine gas pricing. He explained how a missing block in an era could lead to different gas price calculations across nodes. The concern was that missing block utilisation data could lead to incorrect calculations.
>
> Decision/Resolution:
> - Identified that the current calculation should check for unbroken block tracking before computing utilisation.
> - A fix will be implemented to ensure only complete block utilisation data is considered.
>
> Next step:
> - Update utilisation tracking to verify data completeness before calculation.