Add how-to guide for API abstraction levels (NPE/NLE)

[dgedon]

The existing documentation does not explicitly frame abstraction levels as a concept. Functionality for customizing inference is currently scattered across:

• docs/tutorials/00_getting_started.ipynb - Basic usage only
• docs/how_to_guide/03_density_estimators.ipynb - Customization with posterior_nn()
• docs/advanced_tutorials/18_training_interface.ipynb - Custom training loops

Missing: A unified guide showing the progression from simple to advanced API usage and when to use each level.

[Pratyusha-DS13]

Hi! I’m currently contributing to sbi for GSoC 2026 and have been working on documentation improvements.

This looks like a really interesting and impactful addition. I’d love to contribute to it.

I was thinking of starting by drafting a basic structure for the guide (e.g., outlining the different abstraction levels and linking existing tutorials), and then iterating further.

Does that approach make sense, or would you recommend starting with a specific part?

Thanks!

[dgedon]

Hi @Pratyusha-DS13! Thanks for your interest. However, there is already a PR open for this issue (see #1758). So there is no work currently needed on this part.

[BharathC0]

@dgedon can I work on it

for idea 2 the preparation

[janfb]

@dgedon can I work on it

for idea 2 the preparation

Hi @BharathC0 , thanks for offering your help here. Please read the comments above, the issue is already assigned and has an open PR.

[Pratyusha-DS13]

Hi @Pratyusha-DS13! Thanks for your interest. However, there is already a PR open for this issue (see #1758). So there is no work currently needed on this part.

Got it, thanks for letting me know!

I'll take a look at other open issues. Please let me know if there's anything similar where contributions would be helpful.