Added nix flake to repl-session

flake.nix

@@ -0,0 +1,53 @@
+{
+  description = "Python tool to run a given REPL session and evaluate the outcomes";
+
+  inputs.pyproject-nix.url = "github:pyproject-nix/pyproject.nix";
+  inputs.pyproject-nix.inputs.nixpkgs.follows = "nixpkgs";
+  inputs.flake-utils.url = "github:numtide/flake-utils";
+
+  outputs =
+  { nixpkgs, pyproject-nix, flake-utils, ... }: flake-utils.lib.eachDefaultSystem (system:
+  let
+
+    project = pyproject-nix.lib.project.loadPyproject {
+      projectRoot = ./.;
+    };
+
+    pythonAttr = "python3";
+
+    overlay = final: prev: {
+      pythonPackagesExtensions = prev.pythonPackagesExtensions ++ [
+        (python-final: python-prev: { 
+          argh = python-prev.argh.overridePythonAttrs(old: rec {
+            version = "0.30.5";
+            src = python-final.fetchPypi {
+              pname = "argh";
+              inherit version;
+              sha256 = "sha256-s339YXoJ0ZpKe8rtDgYLKIvHrI39wPrPiGpJol/zNyg=";
+            };
+            doCheck = false;
+          });
+          msgspec = python-prev.msgspec.overridePythonAttrs(old: rec {
+            version = "0.20.0";
+            src = final.fetchFromGitHub {
+              owner = "jcrist";
+              repo = "msgspec";
+              tag = "${version}";
+              sha256 = "sha256-DWDmnSuo12oXl9NVfNhIOtWrQeJ9DMmHxOyHY33Datk=";
+            };
+            build-system = [ python-final.setuptools-scm ];
+          });
+        })
+      ];
+    };
+  in
+  let
+    pkgs = import nixpkgs { inherit system; overlays = [ overlay ]; };
+    python = pkgs.${pythonAttr};
+    pythonEnv = python.withPackages (project.renderers.withPackages { inherit python; });
+  in
+  {
+    devShells.default = pkgs.mkShell { packages = [ pythonEnv ]; };
+    packages.default = python.pkgs.buildPythonPackage (project.renderers.buildPythonPackage { inherit python; });
+  });
+}