sdbuildR 2.2.3

• import_insightmaker(), url_to_insightmaker(), and insightmaker_to_json() now fail gracefully, e.g., when internet is not available.

• install_julia_env() no longer rebuilds an environment that is already up to date.
  Use the new install_julia_env(force = TRUE) for a deliberate clean rebuild.

• The Julia environment now installs only the four OrdinaryDiffEq solver
  sub-packages sdbuildR actually uses, rather than OrdinaryDiffEq. This removes
  12 packages from the environment and makes loading faster. In addition,
  PrecompileTools is added as a Julia dependency for faster Julia simulations.Updating to this sdbuildR version thus requires re-running install_julia_env() again.