@spec check(module(), module()) :: :ok | {:violation, atom(), map()}

Check whether a call from caller to callee is allowed.

Returns :ok or {:violation, type, details}.

@spec check_external(module(), atom()) ::
  :ok | {:violation, :externals_restricted, map()}

Check whether a call from caller_context to an external package app is allowed. Returns :ok or {:violation, :externals_restricted, details}.