Format .nix files

This does not include any automation for the release branch, but
is based on the configuration of https://github.com/NixOS/nix/pull/12349

    pre-commit run -a nixfmt-rfc-style

src/external-api-docs/package.nix

@@ -1,13 +1,14 @@
-{ lib
-, mkMesonDerivation
+{
+  lib,
+  mkMesonDerivation,
 
-, meson
-, ninja
-, doxygen
+  meson,
+  ninja,
+  doxygen,
 
-# Configuration Options
+  # Configuration Options
 
-, version
+  version,
 }:
 
 let
@@ -42,11 +43,10 @@ mkMesonDerivation (finalAttrs: {
     doxygen
   ];
 
-  preConfigure =
-    ''
-      chmod u+w ./.version
-      echo ${finalAttrs.version} > ./.version
-    '';
+  preConfigure = ''
+    chmod u+w ./.version
+    echo ${finalAttrs.version} > ./.version
+  '';
 
   postInstall = ''
     mkdir -p ''${!outputDoc}/nix-support