Class EventUtilities

Regenerates event-level stats from the current in-memory event state.

Important behavior:

• Clears ONLY event stats (event.clearStats()).
• Does NOT clear activity stats.
• Does NOT read the original imported file (FIT/TCX/GPX/etc.); raw source payload is not retained.

Regeneration model:

• Single-activity event: copies current activity stats into the event.
• Multi-activity event: recomputes event summary stats from activity stats and aggregates power curves.

Interaction with generateStatsForAll(event):

• generateStatsForAll calls activity generation first (generateMissingStreamsAndStatsForActivity), then calls this method.
• Activity generation is "fill missing", not "replace existing": existing activity stats are preserved.
• If activity stats were cleared or removed by caller code before regeneration, missing stats are recomputed from streams (for example, Average Speed from speed stream mean, Ascent from altitude gain).

Distance behavior:

• Event distance is rebuilt from activities during event summarization.
• Activity distance is recomputed only when missing or equal to zero (in activity generation path).