Add nix flake

Can be removed once we agree on the package management solution.

default.nix

+{ pkgs, lib }:
+
+pkgs.stdenv.mkDerivation rec {
+  pname = "sassena";
+  version = "0.1.0";
+
+  src = ./.;
+
+  nativeBuildInputs = with pkgs; [ ninja python3 cmake clang-tools gcc13 ];
+
+  buildInputs = with pkgs;
+    let boost-mpi = boost.override { useMpi = true; };
+    in [ blas fftw libxml2 zlib boost-mpi hdf5 hdf5-cpp hdf5-mpi mpi ];
+
+  configurePhase = ''
+    mkdir build
+    cd build
+    cmake -G Ninja -DCMAKE_EXPORT_COMPILE_COMMANDS=ON ..
+  '';
+  buildPhase = ''
+    ninja
+  '';
+
+  meta = with lib; { platforms = with platforms; linux ++ darwin; };
+}

flake.lock

+{
+  "nodes": {
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1685566663,
+        "narHash": "sha256-btHN1czJ6rzteeCuE/PNrdssqYD2nIA4w48miQAFloM=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "4ecab3273592f27479a583fb6d975d4aba3486fe",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "23.05",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "nixpkgs": "nixpkgs",
+        "utils": "utils"
+      }
+    },
+    "systems": {
+      "locked": {
+        "lastModified": 1681028828,
+        "narHash": "sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768=",
+        "owner": "nix-systems",
+        "repo": "default",
+        "rev": "da67096a3b9bf56a91d16901293e51ba5b49a27e",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-systems",
+        "repo": "default",
+        "type": "github"
+      }
+    },
+    "utils": {
+      "inputs": {
+        "systems": "systems"
+      },
+      "locked": {
+        "lastModified": 1710146030,
+        "narHash": "sha256-SZ5L6eA7HJ/nmkzGG7/ISclqe6oZdOZTNoesiInkXPQ=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "b1d9ab70662946ef0850d488da1c9019f3a9752a",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "type": "github"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

+{
+  description = "Sassena";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/23.05";
+    utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs = { self, nixpkgs, ... }@inputs:
+    inputs.utils.lib.eachSystem [
+      "x86_64-linux"
+      "i686-linux"
+      "aarch64-linux"
+      "x86_64-darwin"
+    ] (system:
+      let
+        pkgs = import nixpkgs {
+          inherit system;
+          overlays = [ ];
+        };
+      in {
+        devShells.default = pkgs.mkShell rec {
+          name = "sassena";
+
+          nativeBuildInputs = with pkgs;
+            let boost-mpi = boost.override { useMpi = true; };
+            in [
+              clang-tools
+              cmake
+              ninja
+              python3
+              blas
+              fftw
+              libxml2
+              zlib
+              boost-mpi
+              # hdf5
+              hdf5-cpp
+              hdf5-mpi
+              mpi
+            ];
+
+          packages = with pkgs; [
+            gcc13
+          ];
+
+        };
+
+        packages.default = pkgs.callPackage ./default.nix { };
+      });
+}