Consumption forecast via homeassistant sensor

[MaStr]

Keeping track of other issues to be resolved.

Topic came off muexxl/ha_addons#29

[MaStr]

Other commits

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[MaStr]

Currently, the main process is taking care of the initial schedule.
The job is rescheduled after it is done by the global
Scheduler. Currently it is running with "every 10 minutes". Rescheduling happens independent from the duration of the job.

Best scenario may be:

• every forecast type is responsible for themselves in terms of scheduling.
• the forecast schedules the task not with "every" but with at (point in time). That will change the forecast from a general retry but as an "in point" reschedule to the next refresh point.
• problem, take care of possible exceptions that circumvents reschedule at()
• a failsafe refresh at every 10 minutes