feat: add playback speed control and visualization for video segments

[virajbhartiya]

Features Added

• New "Clips" tab in the ConfigSidebar for controlling segment speeds
• Speed presets (0.25x to 4x) and custom speed input
• Visual indicators in the timeline when a clip has modified speed
• Current speed indicator in the player during playback
• Visual styling with blue stripes for clips with non-default speed

Motivation

I've been wanting this feature for so long that I decided to implement it myself! Cap has become an essential tool in my workflow, and the ability to speed up/slow down specific sections will make it even more powerful for creating polished videos.

I love this product and hope this contribution helps make it even better for everyone. Looking forward to your feedback!

[virajbhartiya]

@richiemcilroy @Brendonovich Can you Please take a look at this?

[Brendonovich]

Does this PR actually implement clip retiming or is it just the editor UI?

[virajbhartiya]

Yes it implements the functionality and the editor UI changes

[Brendonovich]

Did you forget to push some code? You've made no changes to the Rust code in charge of playback or exporting that would be necessary to implement this

[virajbhartiya]

Oh yes I had forgotten to push the backend changes

[virajbhartiya]

Pushed the backend changes as well @Brendonovich.

[EricWiener]

Could this be merged?

[EricWiener]

This wasn't working for me and I needed speed editing soon so I added #632 but feel free to use this instead