nix: Clean up files, use good practices

Toolchain/default.nix

@@ -0,0 +1,30 @@
+{ pkgs ? import <nixpkgs> { } }: with pkgs;
+
+mkShell.override { stdenv = gcc13Stdenv; } {
+  packages = [
+    ccache
+    cmake
+    curl
+    e2fsprogs
+    fuse2fs
+    gcc13
+    gmp
+    # To create port launcher icons
+    imagemagick
+    libmpc
+    mpfr
+    ninja
+    patch
+    pkg-config
+    rsync
+    texinfo
+    unzip
+    # To build the GRUB disk image
+    grub2
+    libxcrypt
+    openssl
+    parted
+    qemu
+    python3
+  ];
+}