A tool to convert multipart models to singlepart models

[philpax]

Our new loader does not support multipart models because they do unfun things with tensor strides. Instead of trying to support both loaders indefinitely, it's much simpler to build a tool that will convert a GGML/GGMF multipart model to a GGJT singlepart model. The multipart models are relatively rare, so not having native support shouldn't pose too much of an issue.

[philpax]

This will need to be built on top of #84.

[philpax]

There are some changes in #141 around loading infrastructure. Wait for that one to be merged first.

[philpax]

There are models floating around that aren't fully compliant with the format (e.g. missing scores). This tool could be used as a general-purpose solution for reading in those models with some kind of compatibility mode, fixing them up, and writing a fully compliant GGJT file.

[philpax]

Closing this because multipart GGML models are pretty rare now.