Rows without a parseable string ts share one undated bucket instead of
each escaping the bound; a ts without a zone is read as UTC, so the day
does not depend on the machine's zone; days_span counts the same UTC
days; question_id and user_choice must be strings. Tests pin a zone west
of UTC. CHANGELOG says contributing_events is recorded in the profile
JSON and not displayed yet (#3436).
Co-authored-by: capy-ai[bot] <230910855+capy-ai[bot]@users.noreply.github.com>