easycrypt: fix runtest command

The `ec-runtest` program is still available as a separate
easycrypt-runtest package, but the `easycrypt runtest` command now also
works out-of-the-box.

pkgs/applications/science/logic/easycrypt/default.nix

···
-{ lib, stdenv, fetchFromGitHub, ocamlPackages, why3 }:
+{ lib, stdenv, fetchFromGitHub, ocamlPackages, why3, python3 }:
 
 stdenv.mkDerivation rec {
   pname = "easycrypt";
···
     findlib
     menhir
     ocaml
+    python3.pkgs.wrapPython
   ];
   buildInputs = with ocamlPackages; [
     batteries
···
     substituteInPlace dune-project --replace '(name easycrypt)' '(name easycrypt)(version ${version})'
   '';
 
+  pythonPath = with python3.pkgs; [ pyyaml ];
+
   installPhase = ''
     runHook preInstall
     dune install --prefix $out ${pname}
     rm $out/bin/ec-runtest
+    wrapPythonProgramsIn "$out/lib/easycrypt/commands" "$pythonPath"
     runHook postInstall
   '';