Fix Nix build, add Nix to CI (#840)

* Nix: Reuse input `flake-utils` in `zig-overlay`

* CI/main: convert line endings from `CRLF` to `LF`

* CI: Add Nix build

flake.lock

@@ -1,21 +1,6 @@
 {
   "nodes": {
     "flake-utils": {
-      "locked": {
-        "lastModified": 1667395993,
-        "narHash": "sha256-nuEHfE/LcWyuSWnS8t12N1wc105Qtau+/OdUAjtQ0rA=",
-        "owner": "numtide",
-        "repo": "flake-utils",
-        "rev": "5aed5285a952e0b949eb3ba02c12fa4fcfef535f",
-        "type": "github"
-      },
-      "original": {
-        "owner": "numtide",
-        "repo": "flake-utils",
-        "type": "github"
-      }
-    },
-    "flake-utils_2": {
       "locked": {
         "lastModified": 1659877975,
         "narHash": "sha256-zllb8aq3YO3h8B/U0/J1WBgAL8EX5yWf5pMj3G0NAmc=",
@@ -110,7 +95,9 @@
     },
     "zig-overlay": {
       "inputs": {
-        "flake-utils": "flake-utils_2",
+        "flake-utils": [
+          "flake-utils"
+        ],
         "nixpkgs": [
           "nixpkgs"
         ]