Host pre-built Nix packages binary on Cachix

[mbekkomo]

Allow Nix packages pre-built to be hosted on Cachix. This reduces time for building the Nix packages, especially when it's used in projects that has Nix flake and are using this.

Things that are affected by this:

• Packages in outputs.packages.
• Newly created workflow action to push binaries onto Cachix store (every release).

[CppCXY]

That makes a lot of sense, but why not just use Cargo? Additionally, I am not familiar with Nix-related things; this was brought up by someone else's PR.

[mbekkomo]

Because Nix uses a functional programming approach, where environments are immutable (cannot be modified directly) and packages are built and managed using a declarative configuration file (called a Nix expression). The current environment will be kept until a new configuration is evaluated and is used to "regenerate" a new environment. Cargo on the other hand will "modify it directly" and installs the package right away.