raw meshes: support albedo factors, clean up examples and acknowledge lack of support for .obj

[teh-cmc]

• We already support albedo factors for encoded meshes, so I just piggy backed on that for raw meshes; that way we just punt on any vertex-buffer related questions.
• We used to behave like we support .obj files, except we haven't for a while.
• Fixed all the dataset download mess in the deep_sdf and raw_mesh examples (I hope).

python (./examples/raw_mesh/main.py --scene buggy) vs. rust (cargo r -p raw_mesh -- examples/deep_sdf/dataset/downloaded/buggy/buggy.glb):

23-02-03_17.28.18.patched.mp4

[teh-cmc]

that was fast 👀 thanks!