DES-201: add a YouTube-like event bar

[vyneer]

This PR adds a YouTube-like event bar for subs/donos. The messages stay in the bar for an amount of time that corresponds to the amount of money spent (the exact ratio can be set in the website config, see https://github.com/destinygg/website-private/pull/273). You can see when the event will decay by checking its progress-bar background.

Clicking on the event expands it, showing its details.

The events get added to the bar in the opposite order that they're received (latest ones go first/to the left). I experimented with sorting the events based on the percentage left instead (higher percentage goes first/to the left), but I found the UX to be annoying - sometimes I clicked on one event, only to find chat highlighting another, since it sorted them before I clicked right underneath my cursor. Another issue with that approach was event positions flipping back and forth in rapid succession if they're close in percentages, but decay at slightly different rates.

Some videos showing the bar in action:

Simple donation

2024-03-12.19-01-38.mp4

Interaction with pinned messages

2024-03-12.19-02-19.mp4

To prevent overcrowding of the UI, the expanded/highlighted event temporarily hides the pinned message UI.

Showing persistence

2024-03-12.19-03-06.mp4

Multiple donations

2024-03-12.19-04-32.mp4

Regular subscription

2024-03-12.19-41-30.mp4

Gifted subscription

2024-03-12.19-42-12.mp4

Mass gift

2024-03-12.19-50-44.mp4

Mass gifts only add one event to the bar (the main one), and not every single following sub.

Handling long usernames

2024-03-12.20-45-31.mp4

If a username is a bit too long (>=12 characters), instead of filling the entire bar, it will scroll back and forth within its container.

This PR needs https://github.com/destinygg/website-private/pull/273 and https://github.com/destinygg/chat-private/pull/48 to work.

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