Fix furnace test energy loss for intermediate metalness values#32190

mrdoob merged 7 commits intodevmrdoob/three.js:devfrom

claude/fix-furnace-metalness-energy-011CUpEe92sneu3XqjwzVhAhmrdoob/three.js:claude/fix-furnace-metalness-energy-011CUpEe92sneu3XqjwzVhAhCopy head branch name to clipboard