What function best describes the wāw in wa-l-ṭayru fī wukunātihā?

Imruʾ al-Qays: The Horse’s Speed, Agility, and Similes (Verses 52–58)

• A circumstantial wāw describing the time of departure
• An oath-wāw swearing by the horse
• A wāw of accompaniment making birds objects of an action
• An initial wāw introducing an unrelated story