Boyd Gaming has long sought to keep pace with Station Casinos — its more aggressive and, until recently, more profitable competitor in the suburban Las Vegas casino business — with mixed results. With Station facing imminent bankruptcy court filing, Boyd, the No. 2 locals casino company, has found an opening. On Monday, Boyd pounced with a $950 million offer for most of Station’s casinos, including its Texas, Aliante, Santa Fe and Green Valley Ranch Station casinos and its two Fiesta properties.