GENEVA — The latest U.S.-brokered talks between envoys from Moscow and Kyiv over Russia’s all-out invasion of Ukraine ended Wednesday with no sign of a breakthrough and with both sides saying the talks were “difficult,” as the war’s fourth anniversary approaches next week. The negotiations in Switzerland were the third round of direct talks organized by the U.S., after meetings earlier this year in Abu Dhabi that officials described as constructive but which also made no major headway.