Add nix flake build script (#322)

flake.nix

@@ -0,0 +1,47 @@
+{
+  description = "A Scala project with SBT";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-24.05";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs = { self, nixpkgs, flake-utils, ... }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        pkgs = import nixpkgs {
+          inherit system;
+        };
+        sbt = pkgs.sbt;
+        jdk = pkgs.jdk21;
+        scala = pkgs.scala;
+      in {
+        devShell = pkgs.mkShell {
+          buildInputs = [ sbt jdk scala ];
+          shellHook = ''
+            echo "SBT and Scala environment ready!"
+          '';
+        };
+
+        packages.default = pkgs.stdenv.mkDerivation {
+          name = "flake-vsys-build-with-sbt";
+          src = ./.;
+          buildInputs = [ sbt jdk scala ];
+          buildPhase = ''
+            echo "Building with SBT..."
+
+            sed -i 's/scalaVersion in ThisBuild := "2.12.6"/scalaVersion in ThisBuild := "2.12.18"/' build.sbt
+            sed -i 's/sbt.version=1.1.1/sbt.version=1.9.9/' project/build.properties
+
+            export HOME=~
+
+            sbt packageAll
+          '';
+          installPhase = ''
+            mkdir -p $out
+            cp -r target $out
+          '';
+        };
+      }
+    );
+}