Simplify todo example

[RandomInsano]

Description

Refactored the TODO example for readability and performance. Specifically:

1. When creating the visible list of items, enumerate elements before filtering. This simplifies filtering in state.rs
2. Renamed toggle_all to set_completed to be clearer on intention
3. Renamed toggle to toggle_completed to be inline with set_completed
4. Created new function for state (I'm not sure why I did this, can revert 🙂)
5. Use Vec::retain to remove completed entries

As a newcomer I found it a bit hard to follow all of the iterator work being done in the state.rs file. It seemed that most were because the indexes were calculated after filtration in the view side, and hopefully this PR makes it easier for others.

Checklist

• I have reviewed my own code
• I have added tests

[github-actions]

Size Comparison

examples	master (KB)	pull request (KB)	diff (KB)	diff (%)

✅ None of the examples has changed their size significantly.