render3d: gltf_cached - a still model loaded once by dir, file and node

A game placing props while it plays (a sign an animal leaves, a fish, a bobber) loaded each through
gltf_load, which reads the file and parses its document every time. gltf_cached finds the same
(dir, file, node) by comparing the names in place and hands back the model the first load made;
a model whose document is read after the load (ludic.anim's clips) still goes through gltf_load.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/ludic.render3d/r3d.ludic

@@ -29,6 +29,7 @@ import "post.ludic"
 import "quat.ludic"
 import "gltf.ludic"
 import "gltf_release.ludic"
+import "gltf_cached.ludic"
 import "skin.ludic"
 import "scatter.ludic"
 import "actor.ludic"