Improve the estimation for power consumption of the battery

[Plecra]

PR check-list

• Branch has a clean commit history
• Additional tests are included, if changing behaviors/core code that is testable.
  • At least, I'm not seeing any particularly testable behaviours here, without just defining the test with the new model :D
• Proper Copyright + License headers added to applicable files (Generally, we stick to "The ZMK Contributors" for copyrights to help avoid churn when files get edited)
• Pre-commit used to check formatting of files, commit messages, etc.
• Includes any necessary documentation changes.

Accounting for the effects mentioned in #3223

I've just gone with a simple update to the constants for the underestimated discharge efficiency, the computation is all still accurate.

I've documented the implementation I've used for the battery decay modelling, hopefully clear enough to pass a vibe check :) The changes are quite targeted, I was able to just replace the estimated runtime + battery power consumption.

With the update, the battery's impact on power properly accounts for changes in the configuration of the rest of the board (note the changes in self discharge consumption)!

• 110mAh + nice!nano -> 1 month and 4 weeks

• 110mAh + nice!nano v2 -> 4 months and 5 days

• 2000mAh + nice!nano v2 -> 2 years and 8 months

While the derivation makes sense to me I can't be particularly sure this reflects real world performance, I'd be curious to hear from someone who has tested battery performance in these configurations.