update docs and related tooling

[kMutagene]

This PR will

• [x] update toolchain to use .net 8
• [x] update to fsdocs 20+
• [x] remove all TOCs from docs as they are now generated
• [ ] refactor all docs into notebooks

Note that the docs of this repo are somehow cursed. I managed to fix the integration docs, which are currently not displaying output, but somehow broke signal processing and fit quality docs. I think the only solution for this is moving docs from scripts to notebooks, as they have their own mechanism of embedding output. This has the big advantage of writing docs in notebooks though, with markdown rendering and chart embedding. Disadvantage is that i have to copy paste a lot.

Anyways, @bvenn can you maybe try this out locally? maybe the broken docs output is a local problem?

Here is a side-by-side, left and middle are new theme dark/light, right is old theme: