Mexican state oil giant Pemex was spared a rating downgrade at Moody’s despite the agency slashing Mexico’s sovereign rating to just one notch above junk status. Yet, the affirmation of Pemex’s ratings masks the struggles of the heavily indebted Mexican oil firm, which has failed to deliver profits even as oil prices surged to above $100 in recent months. Moody’s Ratings on Friday affirmed the ‘ca’ standalone credit strength of Petroleos Mexicanos, as Pemex is officially known, as well as the B1 Corporate Family…