Clarify event_count usage and APC data guidance

[chrisyamas]

Summary

This change clarifies the passenger_events.event_count field documentation to provide guidance on proper usage, distinguishing between individual passenger events and aggregated APC counts.

Resolves #236

Changes

• spec/passenger_events.schema.json updated event_count description to:
  • specify that values > 1 should only be used for truly simultaneous events (e.g., parent carrying child through doorway)
  • direct aggregated APC counts to stop_visits table instead, and
  • clarify that a value of 0 indicates a recorded event with no passengers, distinct from null/missing data
• CHANGELOG.md added entry under [Unreleased]

Reason for change

The original description was ambiguous about when to use event_count > 1 vs. recording aggregated data. Some TIDES implementers have noted the lack of clarity for whether to put APC summary data (for instance, "6 passengers boarded at this stop") into passenger_events or stop_visits.

This clarification establishes that passenger_events is for discrete, instantaneous events, while stop_visits is the appropriate destination for aggregated counts.

- For reference, see related discussion in Issue #236 and Fall 2025 TIDES Issues Working Group notes from December 1

Review checklist

Per TIDES change management policy, the following must be met before feature branch changes can merge to develop branch:

• All JSON files validate
• Reviewed and approved by 2+ contributors or board members

[github-actions]

Documentation available at: http://tides-transit.github.io/TIDES/feature/issue-236-event-count