eval: Improve lang server idle detection (#29135)

Brings back #29013 after it was accidentally reverted by
https://github.com/zed-industries/zed/pull/28961/commits/e9bb15b9063615762c866c30aaf646acb12af1f3.

Release Notes:

- N/A
ceeae790b7Agus Zubiaga committed on 4/21/2025, 12:17:28 AM· committed by GitHubparent107d8ca
1 file changedLine totals unavailable