refactor: remove `Future` wrapper type

[mrcjkb]

Now that nio.tests work with busted, we can use nio.control.Future directly, and don't need to use vim.SystemObj:wait().

[github-actions[bot]]

Review Checklist

Does this PR follow the Contribution Guidelines? Following is a partial checklist:

Proper conventional commit scoping:

• For example, fix(installer): some installer bugfix

• [x] Pull request title has the appropriate conventional commit prefix.

If applicable:

• [x] Tested
  • [ ] Tests have been added.
  • [ ] Tested manually (steps in PR description).
• [ ] Updated documentation.