Optimiser fixes, tweak levelling order and fix for charging with solar

What's Changed

Changes made to the optimiser to catch some corner cases:

• Optimise levels from the end of the plan first
• When charging with solar that won't provide the full rate charge account of the additional export of that solar.

• Fix for issue related to metric self sufficiency by @springfall2008 in #1877
• Fixes related to charging with active solar by @springfall2008 in #1878

Full Changelog: v8.11.0...v8.11.1