[DOC] Some love ❤️ for dev docs

[PicoCentauri]

Location of the issue

https://docs.metatensor.org/metatrain/latest/dev-docs/index.html

Description of the issue

We are making the tools and workflows for devs better and better 🎉. We are adding a testsuite (#920), the new rendering of the hypers (#863) or using the metatensor nn.Module (#938). However, I think the docs for devs are still very chaotic and unstructured.

Suggested fix or improvement (optional)

• We should add a general subsection for the Python API
• Move the CHANGELOG somewhere else. This is not really only relevant for devs but evenly or even more relevant for users.
• We could a subsection Developer concepts similar to the user concepts. There goes the Life Cycle of an Architecture, Adding a new architecture, DatasetInformation, new loss function

The new section structure could be

Contrbuting
Python API
Developer Concepts

each with the subsections mentioned above.

The DatasetInformation page also needs some proofreading. Maybe this can also be done with the new rendering in Python (@pfebrer)

Additional context

No response

[pfebrer]

Regarding the CHANGELOGs, there are two kind of changes: the ones that matter to users and the ones that matter to devs. I guess we would have to separate those. Anyway, are we logging the changes in CHANGELOG? I don't think so 😅

[PicoCentauri]

We don't force you to write them and if you don't, we write them for every release based on the PRs.