feat(configurations)!: flatten down, introduce meta.nix

Flatten down directory structure:
- From: `./hosts/${configuration-type}/${system}/{configuration,deploy}.nix`
-   To: `./hosts/${configuration-type}/{meta,configuration}.nix`
Keep `system` and `deploy-rs` config in `meta.nix`
Update `flake.lock`

hosts/nix-darwin/limonka/configuration.nix

@@ -0,0 +1,120 @@
+{ inputs, lib, pkgs, config, ... }:
+
+{
+  environment.systemPackages = with pkgs; [ ];
+
+  # environment.darwinConfig = builtins.toString ./configuration.nix;
+
+  # Auto upgrade nix package and the daemon service.
+  services.nix-daemon.enable = true;
+
+  nix = let
+    flakeInputs = lib.filterAttrs (lib.const (lib.isType "flake")) inputs;
+  in {
+    # Ensure we can work with flakes
+    # TODO: add to `README.md`
+    # NOTE: run `sudo -i nix-env --uninstall nix` to uninstall the global `nix`
+    package = pkgs.nixVersions.monitored.latest;
+
+    # This will add each flake input as a registry
+    # To make nix3 commands consistent with your flake
+    registry = lib.mapAttrs (_: value: { flake = value; }) flakeInputs;
+
+    # This will additionally add your inputs to the system's legacy channels
+    # Making legacy nix commands consistent as well, awesome!
+    nixPath = lib.mapAttrsToList (key: value: "${key}=flake:${key}") flakeInputs;
+
+    # extraOptions = ''
+    #   # Enable flakes and new 'nix' command
+    #   experimental-features = nix-command flakes
+    #   # Allow building multiple derivations in parallel
+    #   max-jobs = auto
+    #   # Deduplicate and optimize nix store
+    #   auto-optimise-store = true
+    #   # Keep outputs and derivations
+    #   keep-outputs = true
+    #   keep-derivations = true
+    # '';
+
+    settings = {
+      # Enable flakes and new 'nix' command
+      experimental-features = [
+        # "nix-command"
+        # "flakes"
+
+        # "no-url-literals"       # Disabling URL literals
+        "ca-derivations"        # Content-Addressable Derivations
+        "recursive-nix"         # Recursive Nix
+        "flakes"                # Flakes and related commands
+        "nix-command"           # Experimental Nix commands
+        "auto-allocate-uids"    # Automatic allocation of UIDs
+        "cgroups"               # Cgroup support
+        # "daemon-trust-override" # Overriding daemon trust settings
+        # "dynamic-derivations"   # Dynamic derivation support
+        # "discard-references"    # Discarding build output references
+        "fetch-closure"         # builtins.fetchClosure
+        "impure-derivations"    # Impure derivations
+      ];
+
+      # Allow building multiple derivations in parallel
+      max-jobs = "auto";
+
+      # Deduplicate and optimize nix store
+      auto-optimise-store = false;
+
+      # Keep outputs and derivations
+      keep-outputs = true;
+      keep-derivations = true;
+
+      trusted-users = [
+        "root"
+        "pavelatanasov"
+      ];
+
+      # Add nix-community and rix101 cachix caches
+      substituters = [
+        "https://rix101.cachix.org"
+        "https://nix-community.cachix.org"
+        "https://lean4.cachix.org"
+        "https://nixpkgs-cross-overlay.cachix.org"
+      ];
+      trusted-public-keys = [
+        "rix101.cachix.org-1:2u9ZGi93zY3hJXQyoHkNBZpJK+GiXQyYf9J5TLzCpFY="
+        "nix-community.cachix.org-1:mB9FSh9qf2dCimDSUo8Zy7bkq5CX+/rkCWyvRCYg3Fs="
+        "lean4.cachix.org-1:mawtxSxcaiWE24xCXXgh3qnvlTkyU7evRRnGeAhD4Wk="
+        "nixpkgs-cross-overlay.cachix.org-1:TjKExGN4ys960TlsGqNOI/NBdoz2Jdr2ow1VybWV5JM="
+      ];
+    };
+  };
+
+  # Create /etc/zshrc that loads the nix-darwin environment.
+  programs.zsh.enable = true; # default shell on catalina
+
+  # Fonts
+  fonts.packages = with pkgs; [
+    (nerdfonts.override { fonts = [ "FiraCode" ]; })
+  ];
+
+  reo101 = {
+    system = {
+      enable = true;
+    };
+    brew = {
+      enable = true;
+    };
+    yabai = {
+      enable = true;
+    };
+  };
+
+  # Keyboard
+  system.keyboard.enableKeyMapping = true;
+  system.keyboard.remapCapsLockToEscape = true;
+
+  # Add ability to used TouchID for sudo authentication
+  security.pam.enableSudoTouchIdAuth = true;
+
+  # Used for backwards compatibility, please read the changelog before changing.
+  # > darwin-rebuild changelog
+  system.stateVersion = 4;
+}