fix: Updated Transformer.#visit to skip visiting VariableDeclarator nodes

[bizob2828]

When I reviewed #41. I ran our integration test suite at newrelic to verify feature parity between rust and the new js version. At that time we hadn't migrated grpc-js. Since the rewrite was merged, we did migrate grpc-js to use orchestrion. It turns out it has some interesting syntax that was handled with the rust version and not in the js.

let Server = (() => {
  class Server {
    register() {}
  }
  return Server
}()

exports.Server = Server

There was more to it but that's the part of the AST that it couldn't locate register and wrap it. This PR fixes it