BEIJING — The Iran war is squeezing a global commodities market already pressured by China's export controls and stockpiling efforts. Prices of three niche elements — tungsten, sulfur and helium — have climbed sharply in recent weeks. While none of the commodities are traded as widely as oil, the surge indicates how ripple effects from the Middle East conflict could end up restricting production of the semiconductors that power artificial intelligence advances. Tungsten, a metal nearly as hard