What is the retained nūn in tubʿidīnī?

Imruʾ al-Qays: Dialogue in ʿUnayzah’s Litter, Boasting, and an Oath (Verses 13–18)

• The indicative nūn retained after prohibition
• Heavy emphatic nūn
• Protective nūn before the first-person object suffix
• The feminine plural nūn