chore: improve Nix flake

nix/shell.nix

@@ -0,0 +1,36 @@
+{ pkgs, rust-toolchain, self, ... }:
+
+{
+  default = pkgs.mkShell {
+    name = "immich-tools";
+    buildInputs = with pkgs; [
+      cargo
+      cargo-edit
+      cargo-insta
+      cargo-machete
+      cargo-release
+      cargo-sort
+      git-cliff
+      openssl
+      pkg-config
+      rustc
+      rust-toolchain
+    ] ++ lib.optionals stdenv.isDarwin [
+      libiconv
+    ] ++ self.checks.${pkgs.system}.pre-commit-check.enabledPackages;
+    RUST_BACKTRACE = 1;
+
+    # Copy rust-toolchain to project directory for easy use in IntelliJ
+    shellHook = ''
+      if [ -L ./.rust-toolchain ] && [ "$(readlink ./.rust-toolchain)" = "${rust-toolchain}" ]; then
+        echo "Rust toolchain symlink is already correct."
+      else
+        rm -f ./.rust-toolchain
+        ln -s ${rust-toolchain} ./.rust-toolchain
+        echo "Rust toolchain symlink updated."
+      fi
+
+      ${self.checks.${pkgs.system}.pre-commit-check.shellHook}
+    '';
+  };
+}