Closes #40019

Follow-up https://github.com/zed-industries/zed/pull/40025

This PR reduces/removes the flickering of inlay colors. This is done by
adding a debounce, and not detaching the task that fetches the new
colors.

**Result**


https://github.com/user-attachments/assets/5dae278b-b821-4e64-8adb-c4d8376ba1df

Release Notes:

- Lsp colors: Reduce flickering while typing.

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Co-authored-by: Kirill Bulatov <kirill@zed.dev>