Select SoC value before schedule start

[Ahmad-Wahid]

I think we'll need some sort of inference here, e.g. in case the last SoC value was a couple of minutes before start. One possibility: something like sensor.search_beliefs(most_recent_event=True, events_before=start). Possibly with a events_after=start-max_staleness if we don't want the last SoC value to be unacceptably old.

Originally posted by @Flix6x in #1018 (comment)

I'd leave it None for now, in which case the filter for `events_after' can be left out. [...] we can discuss where this max_staleness parameter should live.

Originally posted by @Flix6x in
#1018 (comment)

[nhoening]

Work on saving SoC values continues in #1018 now, actually