Post-package-split fallout

See merge request !3

Upgrade nixpkgs, use GHC 9.6.6, make it build with cabal

Closes #3

See merge request !1

This commit splits the project in 3 sub-projects:

1. `gargantext-graph-core`: it contains the plain algorithms on graphs;
2. `gargantext-graph-accelerate`: accelerate utilities on graphs;
3. `gargantext-graph-eigin`: eigen utilities on graphs;

Align side branch with main master

See merge request !2