Renders start–end; when both fall on the same day (per isSameDay), the end's date is omitted (only its time is shown). includeDuration appends a formatted duration in parentheses; includeWeekday prefixes each endpoint with an abbreviated weekday name. Each endpoint formats like FormattedDateTime (fi/sv identical, no Intl); non-fi/sv locales separate the two endpoints with non-breaking spaces around the dash.
Helpers used directly: isSameDay(start, end) for the same day range above is true; formatDuration(start, end) gives "2 h 30 min"; and formatDurationMinutes(135) gives "2 h 15 min".