feat: Chapter image trickplay/timeline fallback

[matt-hb]

Pull Request Description

First actual feature PR, chapter images (or lack thereof) have been bothering me a bunch so I'm implementing a trickplay fallback as per #875 .
Also added caching for trickplay images, because we're fetching them a bunch.

Issue Being Fixed

Placeholder when there are no chapter images available, either via fallback to trickplay images or a timeline if trickplay images are not available either.

Screenshots / Recordings

Before (yucky placeholders):

After (with trickplay fallback):

After (with timeline):

hovering a chapter fills the bar up to the selection with a nice animation

Tested On

• Android
• Android TV
• Desktop
• Web

Checklist

• Check that any changes are related to the issue at hand.
• Create timeline widget

[PartyDonut]

Just did a test for Android TV it's quite blurry. Does not look great to be honest.

Another solution would be to change the filterquality inside of the _TrickplayPainter from trick_play_image.dart

[matt-hb]

Another solution would be to change the filterquality inside of the _TrickplayPainter from trick_play_image.dart

Good call, I misunderstood low level drawing and size inheriting before, but after checking this is in fact a lot better.

[matt-hb]

I think the final implementation of the timeline is quite nice, do we think some people would prefer it over having an image for the chapters altogether? If so, I could add a toggle in the options to force it over the images, let me know.

Thanks for all the work over the last couple months, btw! I haven't stopped using the client even though I've not had the time to contribute or finish a PR 😅