KHALID ABDELAZIZ, NAFISA ELTAHIR and AIDAN LEWIS ALARMED that movements of rival military factions in Sudan could bring bloodshed, a group of mediators pushed for last-ditch talks between army chief Abdel Fattah al-Burhan and paramilitary commander General Mohamed Hamdan Dagalo two weeks ago. But neither of Sudan's two most powerful men showed up to the meeting, convened at presidential offices in central Khartoum at 10 a.m. on April 15, three of the Sudanese mediators said, in details revealed for the first time here. Instead, fighting was breaking out across the country. At about 8.30 a.m. shooting started at the Soba military camp…