Update all components in exercises/solutions to use default exports

[kevinb-khan]

Summary:

This will avoid situations where the exercise could be using the original named export even though the developer has memoized the component.

This PR also updates the eslint settings so that devs don't see warnings about certain patterns not working with HMR.

I've also modified the solution in lesson 4 to be even more performant.

Issue: None

Test plan:

• yarn dev
• see that the site renders without error
• check that lesson 4 behaves as expected with the solution being even more performant than before

[beaesguerra]

Looks good to me!

[beaesguerra]

I was poking around some more! We don't use the arePropsEqual arg here because none of the props are objects or functions, right?

Also, since the Fib component is memoized now, I was thinking the component wouldn't re-render if the props (the n value) didn't change. The visual rendering feature shows that the Fib component gets re-rendered whenever the button is pressed, but the profiler says the Fib component wasn't re-rendered. So the visual rendering feature might not be accurate at times!

Screen.Recording.2024-07-03.at.1.35.35.PM.mov

[kevinb-khan]

Interesting. I'll have a closer look tomorrow. Thanks for the video recording.

[kevinb-khan]

I'm seeing the same behaviour. I'll make a note about it in the preliminaries.