perf: defer UI updates away from input logic (@miodec)

[Miodec]

Together with #7119, input handling is 3x faster. Achieved by:

• deferring all UI updates to when the browser is ready and debouncing ui calls.
• using vanilla js where needed
• caching dom elements
• disabling expensive checks if the timer is slow
• switching to a timer that uses RAF instead of setTimeout
• moving some code around

This should make the site smother on slower devices and fix lag spikes causing weird test data.