Release 4.3.0

Added

• Optional ON CONFLICT DO NOTHING race backstop in upsertMutation.
  Pass { onConflict: 'DO NOTHING' } to append ON CONFLICT DO NOTHING
  to the generated INSERT (default: omitted, so existing output is
  unchanged). This is a complement to the always-present
  WHERE NOT EXISTS, not a replacement: WHERE NOT EXISTS still prevents
  serial/bigserial sequence churn, while ON CONFLICT DO NOTHING closes
  the concurrency race where two writers both pass the not-exists check
  and then collide on the unique constraint. It only affects the insert
  half.

Changed

• Generated SQL now uses uppercase keywords (SELECT, INSERT INTO,
  WHERE NOT EXISTS, IS DISTINCT FROM, …) across updateMutation and
  upsertMutation. Purely cosmetic — the statements are semantically
  identical — but any test or snapshot asserting on the old lowercase
  output needs updating.