Someone on discord did, I didn't. He says that he looked at the bytes, did some analysis and created a script for it. I don't think there is currently any way to decode any of those files. But I viewed the files in hex viewer and the MDL appears to be for the model, the MDP appears to be for physics...

With help, I was able to unpack the grp file. But I dunno about the tgp file tho. The grp file further contains even more files. It contains five more files - MDL, MDF, MDP, TFH and TFD. Here's the unpacked grp file along with the script https://drive.google.com/file/d/1CmMSbxtt7kCOYoTFRG33c0R5gYdYj...

A while later, I'd also like to decompile the models and textures, but there is only one mdl file now instead of three among others. The mdl file appears to be a tcf model. I'd also like to know how to open the other files.

2 years later, I too would like to decode the assets. Have you found any way to do so? I'd love to hear it.