chore(nix): add nix flake

.envrc

@@ -0,0 +1,2 @@
+#! /usr/bin/env bash
+use flake

flake.lock

@@ -0,0 +1,25 @@
+{
+  "nodes": {
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1735471104,
+        "narHash": "sha256-0q9NGQySwDQc7RhAV2ukfnu7Gxa5/ybJ2ANT8DQrQrs=",
+        "rev": "88195a94f390381c6afcdaa933c2f6ff93959cb4",
+        "revCount": 729683,
+        "type": "tarball",
+        "url": "https://api.flakehub.com/f/pinned/NixOS/nixpkgs/0.1.729683%2Brev-88195a94f390381c6afcdaa933c2f6ff93959cb4/01941664-52c7-796b-8e68-76474453a95d/source.tar.gz"
+      },
+      "original": {
+        "type": "tarball",
+        "url": "https://flakehub.com/f/NixOS/nixpkgs/0.1.%2A.tar.gz"
+      }
+    },
+    "root": {
+      "inputs": {
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

@@ -0,0 +1,38 @@
+{
+  description = "A Nix-flake-based C# development environment";
+
+  inputs.nixpkgs.url = "https://flakehub.com/f/NixOS/nixpkgs/0.1.*.tar.gz";
+
+  outputs =
+    { self, nixpkgs }:
+    let
+      supportedSystems = [
+        "x86_64-linux"
+        "aarch64-linux"
+        "x86_64-darwin"
+        "aarch64-darwin"
+      ];
+      forEachSupportedSystem =
+        f:
+        nixpkgs.lib.genAttrs supportedSystems (
+          system:
+          f {
+            pkgs = import nixpkgs { inherit system; };
+          }
+        );
+    in
+    {
+      devShells = forEachSupportedSystem (
+        { pkgs }:
+        {
+          default = pkgs.mkShell {
+            packages = with pkgs; [
+              dotnet-sdk
+              omnisharp-roslyn
+              mono
+            ];
+          };
+        }
+      );
+    };
+}