don't send full range updates if old range overlaps new range

[owobred]

Changes

The websocket proxy will now send smaller updates when changing from a smaller window to a larger one.

For example, moving from a window of 0..=5 -> 0..=7 would previously send all of 0..=7, whereas it only actually needs to send 5..=7 to fill the empty space.

|---|
|-----|
     ^^ only these would get sent

The following updates remain the same, this just means that much less gets sent with the current scrolling system.

Checklist

• My code compiles
• I have committed all the files needed to build the project (check if your file is found in .gitignore)
• If I'm introducing a new step in the build process, I have documented / automated it
• I have tested my changes (minimally with one Twitch VOD)

To-do list

• Test that this works as expected, and I haven't made it accidently miss out sections in certain cases
• Test that this doesn't cause issues with the frontend