add Nix flake development environment

.gitignore

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+sandbox/

flake.lock

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+{
+  "nodes": {
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1757810152,
+        "narHash": "sha256-Vp9K5ol6h0J90jG7Rm4RWZsCB3x7v5VPx588TQ1dkfs=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "9a094440e02a699be5c57453a092a8baf569bdad",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixos-25.05",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

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+{
+  description = "devshell-dorne";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-25.05";
+  };
+
+  outputs = inputs @ {
+    self,
+    nixpkgs,
+  }: let
+    defaultSystems = ["aarch64-darwin" "aarch64-linux" "i686-linux" "x86_64-darwin" "x86_64-linux"];
+
+    forAllSystems = f:
+      nixpkgs.lib.genAttrs defaultSystems (system:
+        f system (import nixpkgs {
+          inherit system;
+          overlays = builtins.attrValues self.overlays;
+        }));
+  in {
+    overlays.default = final: prev: {
+    };
+
+    devShells = forAllSystems (
+      system: pkgs: {
+        default = pkgs.mkShell {
+          packages = with pkgs; [
+            gnumake
+
+            # C Compiler & Runtime
+            gcc
+            glibc.dev
+            # C Development Tooling
+            clang-tools
+            bear # clang compile_commands.json
+            valgrind # memory debugging+profiling
+
+            # .NET Compiler & Runtime
+            (with dotnetCorePackages;
+              combinePackages [
+                sdk_9_0
+                runtime_9_0
+              ])
+            # .NET Development Tooling
+            ilspycmd
+          ];
+
+          shell = "${pkgs.bash}/bin/bash";
+
+          # so I can easily read the glibc header files
+          GLIBC = "${pkgs.glibc.dev}/include";
+        };
+      }
+    );
+  };
+}