Main updates v0.2.0 --> v0.3.0: Muon support for AnnData struct and I/O
- added Muon.jl dependency and switched to the Muon AnnData struct
- adapted all data loading and preprocessing functions to the Muon AnnData struct
- many bugfixes in preprocessing functions for subsetting, filtering, HVG selection, transformations
- extension of preprocessing functionality
- comprehensive test cases