Are the "rida" (upper garment) and "izar" (lower garment) among the attributes of Allah, and does this contradict the Oneness of Allah Almighty, given that they might be believed to be separate from His essence, Glory be to Him?

Pride and greatness are two attributes specific to Allah Almighty; it is not permissible for any created being to contend with Him regarding them. The mention of the 'izaar' (waist-wrapper) and 'ridaa'' (cloak) in the hadith (definition) does not mean that Allah has an 'izaar' and 'ridaa'' of the kind that are worn. Rather, it is to emphasize Allah's exclusive possession of these two attributes, and that pride is a veil that prevents the seeing of Allah, just as a cloak veils. Pride and greatness are inherent necessities of Allah's essence; it is not correct to say that He became characterized by them after not having been so.