Reduction and reporting of inverter writes, optimiser changes

What's Changed

CAUTION Some fairly major changes here so its possible I broke something!

Register write improvements

Regarding the potential issue of Predbat creating too many register writes for your inverters flash memory:

• Added a new entity to counter the total register writes so users can check their configuration and report and issues. An average of one every 5 minutes (288 a day) should be fine. If you are seeing much higher than this then please report it.

• Count inverter register writes, reduce writes in some cases, tweak optimiser by @springfall2008 in #1672
• Don't adjust charge/discharge rate if timed pause is supported by @springfall2008 in #1673
• Reduce register writes during low power mode by @springfall2008 in #1676
• Low power mode fixes, new margin control for low power mode by @springfall2008 in #1677

Features

Added a new setting to control the number of minutes margin in low power mode

Optimiser changes

30-minute charge slots are now either on, off or freeze. The charge % target will not be calculated for 30 minute slots. The percentage target is still calculated for larger slots (combine charge = True).

Please feedback on this change, if it causes other issues I may need to revert it.

Fixes

• Fix typo in Octopus, catch traceback to status entity debug by @springfall2008 in #1656
• Fix download list by @springfall2008 in #1657
• Fix discharge time bug, unit testing, add missing file by @springfall2008 in #1660
• Don't enable scheduled charge during export by @springfall2008 in #1669
• Fix some warnings with index out of range by @springfall2008 in #1674

Code improvements

• Split code up into more files, remove old sanity check function by @springfall2008 in #1655
• Coverage run scripts by @springfall2008 in #1658
• unit testing updates by @springfall2008 in #1670

Full Changelog: v8.7.2...v8.8.0