Avg rates now get stored to survive reboot & added unit of measurement

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🎉 HACS repository validator action summary 🎉 ✅ The repository is not archived ✅ manifest.json file exist ✅ All required keys are present in manifest.json ✅ hacs.json has the 'name' key set ✅ The repository has a description ✅ octopusagile is added to https://github.com/home-assistant/brands NICE! ✅ The repository has topics ✅ The repository has issues enabled ✅ This day ends with an 'y' (Monday) ✅ README.md exists ✅ HACS load check