There’s a single-take sequence in “Inside the Yellow Cocoon Shell” that, over roughly 20 minutes and less than a mile’s journey, seems to distill a small corner of eternity. We are somewhere in the Vietnamese countryside, where a soft-spoken young man named Thiên (Le Phong Vu) is sent on an errand by a friend. A different filmmaker might have cut straight to the errand, or perhaps the outcome of the errand, or even kept the errand and this entire conversation about the errand off-screen. But the director, Phạm Thiên Ân, does none of these things. Instead he reminds us that even the most seemin…