feat(ci): cache overlaid packages

ci/common.nix

@@ -0,0 +1,47 @@
+{
+  lib,
+  channels,
+  config,
+  ...
+}: {
+  nixpkgs.args = {
+    localSystem = "x86_64-linux";
+    config = {
+      allowUnfree = true;
+    };
+  };
+
+  ci = {
+    version = "v0.7";
+    gh-actions = {
+      enable = true;
+    };
+  };
+
+  /*nix.config = {
+    extra-platforms = ["aarch64-linux" "armv6l-linux" "armv7l-linux"];
+    #extra-sandbox-paths = with channels.cipkgs; map (package: builtins.unsafeDiscardStringContext "${package}?") [bash qemu "/run/binfmt"];
+  };*/
+
+  channels = {
+    nixfiles.path = ../.;
+    nixpkgs.path = "${channels.nixfiles.inputs.nixpkgs}";
+  };
+
+  ci.gh-actions.checkoutOptions = {
+    submodules = false;
+  };
+
+  cache.cachix = {
+    arc = {
+      enable = true;
+      publicKey = "arc.cachix.org-1:DZmhclLkB6UO0rc0rBzNpwFbbaeLfyn+fYccuAy7YVY=";
+      signingKey = null;
+    };
+    gensokyo-infrastructure = {
+      enable = true;
+      publicKey = "gensokyo-infrastructure.cachix.org-1:CY6ChfQ8KTUdwWoMbo8ZWr2QCLMXUQspHAxywnS2FyI=";
+      signingKey = "mewp";
+    };
+  };
+}