Refactor to depend on new sbi 0.20.0

[janfb]

refactor sbi run scripts to match the new API of sbi version >=0.20.0.

• [x] depend on newest sbi version 0.20.0 to support passing TransformedDistributions as prior
• [x] run all tests.

[janfb]

ready for review @jan-matthis

[janfb]

Thanks for the feedback!

I remove a couple of test files and refactored them into one single sbi test file: test_sbi_run_methods.py

That tests now also inclused sl.

[janfb]

I also changed the requirement to sbi>=0.20.0, as we will likely release a new version that incluces BNRE and SNRE_C soon.

Or do you prefer to fix the setup to one specific sbi version?

[jan-matthis]

Thanks!