Added #[wasm_bindgen] for all mentions of impl Universe

[Yug34]

Summary

Explain the motivation for making this change. What existing problem does the pull request solve? 🤔

The first mentions of impl Universe don't have #[wasm_bindgen], this results in cargo build running successfully but the wasm_game_of_life.d.ts file containing only this type def for Universe:

export class Universe {
  private constructor();
  free(): void;
}

#[wasm_bindgen] is added later, which works perfectly! But admittedly, while studying the code, I didn't read the code outside of impl Universe, and had to spend time debugging and wondering why the d.ts file is correct for greet() but not Universe.

Might save the time for some other people as well; making sure the #[wasm_bindgen] is not missable!