breaking(deps): move from nanomsg to nng

We would like to use IPC communication during testing, so that we
can leverage indpendent test runs. However, the implementation turned
out to be buggy in the now-unmaintainted `nanomsg`.

nix/pkgs.nix

@@ -42,7 +42,7 @@ rec {
     libffi
     libpqxx
     libsodium
-    nanomsg
+    nng
     nil  # nix language server
     pcre
     pkg-config
@@ -50,6 +50,8 @@ rec {
     stdenv.cc.cc
     xz
     zlib
+    zeromq
+    curl
   ] ++ ( lib.optionals stdenv.isDarwin [
        darwin.apple_sdk.frameworks.Accelerate
        ]);