NEVSKE, Ukraine — In a tiny village in eastern Ukraine at the epicenter of the next phase of the war, Lyudmila Degtyaryova measures the Russian advance by listening to the boom of incoming artillery shells. There are more and more of them now. And they are coming more frequently, as Russian troops grind their way forward. “You should see the fireworks here,” said Degtyaryova, 61, as the sounds of artillery howled all around. “It is like New Year’s.” Russia’s military is preparing to launch a new offensive that could soon swallow Degtyaryova’s village of Nevske, and perhaps much more in...