Multi-inverter fixes, car charging, plan optimiser fix

What's Changed

Bug fixes

• When the car is fully charged it shouldn't freeze the battery by @springfall2008 in #1819

Take into account when the car battery is full and no longer freeze the battery.

• Multi-inverter tweaks by @springfall2008 in #1820
• Further multi-inverter tweaks by @springfall2008 in #1822

Fix bugs in multi-inverter handling around charge hold

• Fix bug where sometimes full charge is not selected to maximise export by @springfall2008 in #1825

Sometimes a full charge was not selected even if it was profitable due to additional export.

Full Changelog: v8.8.19...v8.8.20