build: added shell.nix and direnv integration

.envrc

@@ -0,0 +1 @@
+use nix

.gitignore

@@ -1,4 +1,5 @@
 /target
+/.direnv
 
 flamegraph.svg
 perf.data*

shell.nix

@@ -0,0 +1,40 @@
+let
+    nixpkgs = builtins.fetchGit {
+        name = "nixos-23.11";
+        url = "https://github.com/nixos/nixpkgs";
+        ref = "refs/heads/nixos-23.11";
+    };
+
+    nixpkgs-unstable = builtins.fetchGit {
+        name = "nixos-unstable";
+        url = "https://github.com/nixos/nixpkgs";
+        ref = "refs/heads/nixos-unstable";
+    };
+
+    pkgs = import nixpkgs {};
+    pkgs-unstable = import nixpkgs-unstable {};
+
+in pkgs.mkShell {
+    nativeBuildInputs = with pkgs; [
+        pkgs-unstable.rustc
+        pkgs-unstable.rustfmt
+        pkgs-unstable.cargo
+        pkgs-unstable.clippy
+
+        gcc
+        cmake
+        pkg-config
+    ];
+
+    buildInputs = with pkgs; [
+        gtk4
+        glib
+        gdk-pixbuf
+        gobject-introspection
+
+        libadwaita
+    ];
+
+    RUST_SRC_PATH = "${pkgs-unstable.rust.packages.stable.rustPlatform.rustLibSrc}";
+    RUST_BACKTRACE = 1;
+}