Bottles next client implementation

[hotplugindev]

I found some early implementations in the bottles-next Rust project, including initial versions of the CLI and server.

On the main project page, there is also a description of a Rust client built with libcosmic. I wanted to start getting involved with the project, so I made an initial attempt at providing a Nix flake for the bottles-next repository. The goal was to support both installation and local development for the subprojects contained in the repo.

However, while looking through the repository, I could not find the libcosmic client mentioned on the main page.