Api returning null data in the route 'kpi/averageTimeAllDishes'

[Xantass]

Describe your changes

improve average preparation time calculations and enhance dish forecasting logic in KpiService

How to test the feature

Create an order with two food, go to the kds and make one food ready and check if the data time is ok

Issue ticket number and link

#186

Checklist before requesting a review

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have performed a self-review of my code
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Documentation has been updated as required
  If a single item in this checklist is not checked, the pull request cannot be accepted