Nix flake (#758)

* Added Flake for nix

* Removed Cargo lock from ignore

As it's now reccomended by rust team to keep it in repo as well as nix
needs it fetch dependacies for nix run

* Added Nix Compatbilty for package

I forgot to add it that's why this commit is here.

* Made flake minimal

flake.nix

@@ -0,0 +1,52 @@
+{
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+    flake-parts.url = "github:hercules-ci/flake-parts";
+    flake-compat.url = "https://flakehub.com/f/edolstra/flake-compat/1.tar.gz";
+    rust-overlay = {
+      url = "github:oxalica/rust-overlay";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
+  };
+
+  outputs = inputs@{ nixpkgs, flake-parts, ... }:
+    flake-parts.lib.mkFlake {inherit inputs;} {
+      systems = nixpkgs.lib.systems.flakeExposed;
+      perSystem = {
+        pkgs,
+        system,
+        ...
+      }:
+      let
+        rustToolchain = pkgs.rust-bin.fromRustupToolchainFile ./rust-toolchain.toml;
+        manifest = (pkgs.lib.importTOML ./pumpkin/Cargo.toml).package;
+      in
+      {
+        formatter = pkgs.nixfmt-rfc-style;
+        _module.args.pkgs = import nixpkgs {
+          inherit system;
+          overlays = [
+            (import inputs.rust-overlay)
+          ];
+        };
+
+        devShells.default = pkgs.mkShell
+        {
+          nativeBuildInputs = with pkgs; [
+            rustToolchain
+            pkg-config
+          ];
+        };
+
+        packages.default = (pkgs.makeRustPlatform {rustc = rustToolchain; cargo = rustToolchain;}).buildRustPackage {
+            pname = manifest.name;
+            version = manifest.version;
+
+            useFetchCargoVendor = true;
+            cargoLock = {
+                lockFile = ./Cargo.lock;
+            };
+        };
+      };
+    };
+}