add test data

[atlv24]

this might be too much test data, open to suggestions.

the most important test here is doomcone.obj, apparently: it is 22kb and currently fails. if i merge vertices in blender it no longer fails, suggesting something is wrong with the weld_vertices rewrite.

[Elabajaba]

What about adding a dev-dependency on eg. zstd and compressing the models?

edit: Quick test using the zstd cli at a few different compression levels for all the models combined (none is uncompressed):

none:     3,968,622 bytes
level 3:  1,157,252 bytes
level 12: 1,039,909 bytes
level 19: 856,175 bytes