Block teachers' slots from their preferences on limited-oversight dates

Requires permission: ParentsEvening

For each limited-oversight date of the evening and each teacher's preference on it, replaces the teacher's unavailability on that date with the slots the preference rules out: those starting outside its window, and, with includeBreaks, those starting in its break. The times are the evening's own (GET/PUT /ParentsEvening/{id}/PreferenceTimes), or the legacy ones where it has not set them.