TEHRAN, IRAN — China, Iran and Russia conducted joint naval drills Tuesday in the Middle East, offering a show of force in a region still uneasy over Tehran’s rapidly expanding nuclear program and as Yemen’s Houthi rebels threaten new attacks on ships. The joint drills, called the Maritime Security Belt 2025, took place in the Gulf of Oman near the strategic Strait of Hormuz, the narrow mouth of the Persian Gulf through which a fifth of the world’s crude oil passes. The area around the strait has in the past seen Iran seize commercial ships and launch suspected attacks in