Closes#175.

This PR transforms *Iterator classes to actual iterators (before they were justiterables).

PR checklist:

• Make sure to open an issue as abug/issue before writing your code! That way we can discuss the change, evaluate designs, and agree on the general idea
• Ensure the tests and linter pass
• Code coverage does not decrease (if any source code was changed)
• Appropriate docs were updated (if necessary)