Reintroduce caching with a limit

[micahmo]

Pull Request Description

PR #463 introduced caching for ExtendedImage. PR #576 reverted that change. While we have done several things to reduce the jankiness of reloading images (e.g., removing Hero, removing spinners, calculating height), there are still some times when the image reloads unexpectedly and it can be a bit jarring/annoying. One such example is when marking a post as unread, of all things. There's also still the "issue" where if you scroll out of frame and scroll back, all the images have to reload again (discussed here). Finally, there is some discussion in #487 that caching may help to prevent that issue as well.

In this PR, I have first of all set clearMemoryCacheWhenDispose back to false. But more importantly, I have also set cacheMaxAge to 1 minute. This should give us enough time that common operations (scrolling up/down, marking unread) will show the cached image, but the cache will also expire relatively quickly so that prolonged usages of the app will not maintain more than a minute's worth of image cache. (And of course, we can discuss this value.)

Let me know your thoughts on this approach! And maybe we can do some profiling too.

Issue Being Fixed

Issue Number: N/A

Screenshots / Recordings

Before

qemu-system-x86_64_G4DuwK9joB.mp4

After

qemu-system-x86_64_XuEKvBe4be.mp4

Checklist

• Did you update CHANGELOG.md?
• Did you use localized strings where applicable?
• Did you add semanticLabels where applicable for accessibility?

[hjiangsu]

It looks good! I'm still a bit wary about re-introducing the clearMemoryCacheWhenDispose change because it had issues in the past where memory would not be cleared and it would result in a memory leak.

However, we can go ahead and profile this again and check how it performs. I'll keep this on hold until the general release so that we don't introduce this right away if thats good with you!

[hjiangsu]

I'll go ahead and merge this sooner so that we can get feedback from the nightly builds!

[micahmo]

Reporting back after daily driving this for a while... Unfortunately setting cacheMaxAge seems to have an unintended side effect which is that the cache is invalidated after the given time period even if the widget is not disposed! That means, for example, if you're reading comments for a while and then navigate back to the main page, all the images reload. 😞

I would like to investigate this some more, because I would like the cache to be maintained as long as the widgets are not disposed, but also keep the cache around for a little if they are.

That said, if there isn't a nice solution by the time the next release comes around, I'd rather roll this back than have the current behavior lol.