RooUnfoldSpec: produce json configs for PLU
This MR adds functionality to RooUnfoldSpec that allows it to create configuration files for Profile Likelihood Unfolding. This contains a lot of additional bugfixes, including:
- improved (bugfixed) density handling
- improved error handling for misconfigurations of vector and matrix sizes
- expanded tests with underflow and overflow bins
- fixed reference files for CI
- switching to newer ROOT version in CI
- improved handling of function overloads (code deduplication)
- renaming of internal helper functions to reduce confusion
- allow tolerance settings for SVD unfolding
Edited by Carsten Burgard