Autocomplete: Split debounce into two chunks, race the second part with the context retrieving

[philipp-spiess]

This PR splits the debounce time into two logical chunk. The first 25ms (regardless of how long the debounce time is defined), the behavior will be like it is now: We batch events and don't do any concurrent work.

However after 25ms (which, remember, was the debounce time we had until recently), we start to fetch the context in parallel. The idea is that we have shave off up to 50ms from the context retrieval time.

Here's a visualization of a trace:

As you can see in this specific example, context retrieval could almost be free.

One caveat here is that this will increase CPU pressure (since we start fetching context a bit earlier). That's why I think 25ms is a good value for this since we have used it in the past with the same retrieval algorithm quite successfully.

Test plan

• Ensure AC still works
• Check out a trace, e.g.:

[valerybugakov]

Nice!