Further tweaks to SOC Keep handling & export control

What's Changed

Changes

Changed the way best_soc_keep works to gradually fade in the keep metric over a 4 hour period rather than ignore the keep for 4 hours and then fade in over 2 hours.

Changed the export logic to only stop when the SOC is at or below the target rather than based on going below the target.

• Try to export everything left if allowed by @springfall2008 in #1790

### Bug fixes

• Fix issue with battery_scaling and soc_percent by @springfall2008 in #1789

Full Changelog: v8.8.14...v8.8.15