People are fully visible behind small trees


When a party member is behind a 'tree_small' feature, their sprite is layered fully on top of the tree sprite, instead of fading one of the sprites, which happens for larger sizes of tree.

Search the Rust codebase for the `tree_small` feature and the sprite-layering logic used by larger trees. Reproduce the issue with a party member behind a small tree, then compare its rendering behavior with larger tree sizes. Done means the party member is no longer fully visible and the appropriate sprite fading occurs consistently.

Written by the indexing model from the issue text.