Remove the paratest detection.
I consider paratest only for CI and executing a huge set of tests.
But I use vim-test only to execute a single test file or single test.
This eases maintenance as I don't need to commit and push one repo, and
update rev and sha in here.
Instead I can just change configuration and run home-manager switch.
I managed my setup manually.
This commit ports the existing setup to home-manager.
The program module is used to install neovim together with plugins.
Custom plugins are now maintained at Gitea / GitHub and loaded via nix as well.