_get_cached_intervals() used fixed-offset datetimes from fromisoformat()
for iteration. When start and end boundaries span a DST transition (e.g.,
+01:00 CET → +02:00 CEST), the loop's end check compared UTC values,
stopping 1 hour early on spring-forward days.
This caused the last 4 quarter-hourly intervals of "tomorrow" to be
missing, making the binary sensor "Tomorrow data available" show Off
even when full data was present.
Changed iteration to use naive local timestamps, matching the index key
format (timezone stripped via [:19]). The end boundary comparison now
works correctly regardless of DST transitions.
Impact: Binary sensor "Tomorrow data available" now correctly shows On
on DST spring-forward days. Affects all European users on the last
Sunday of March each year.
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