`qmat` switch (#445)

* Some fixes for new numpy version

* Fix for Allen-Cahn project

* Update environment.yml

* TL: added qmat dependency in env files

* TL: corrected pyproject.toml

* TL: full qmat integration

* TL: adapted numpy2 changes

* TL: of course ...

* TL: fixing tests ...

* TL: fix projects dependencies

* TL: still adapting to numpy2

* TL: still fixing project tests ...

* TL: minor change to trigger CI

* TL: opening Pandora's box ...

* TL: ty linting

* TL: adding a note

* TL: corrected bugged reference data for parallelSDC_reloaded

* TL: trying stuff for parallelSDC tests

* TL: investigating

* TL: adapted to new qmat version

* TL: let's stop beeing stupid

* TL: ... starting now

* TL: checking hypothesis

* TL: RK sweeper based on qmat

* TL: oh, thanks black !

* TL: partial solution for parallelSDC tests

* TL: back to partial working version

* TL: trying another idea

* TL: trying this

* TL: no covering for (problematic) ploting function for parallelSDC

* TL: finalized qmat-switch with correct naming for core sub-packages

* TL: omg

* TL: minimum version for qmat dependencies

* TL: minor fixes

* Update collocation.py

* Update collocation.py

* Update sweeper.py

* TL: minor corrections following @pancetta's comments

---------

Co-authored-by: Thomas Baumann <39156931+brownbaerchen@users.noreply.github.com>
Co-authored-by: Robert Speck <pancetta@users.noreply.github.com>