Revert "lsp: Do not reuse disk-based diagnostics (#46437)" (#46487)

This reverts commit dd43891521484dc25d520e3c1551d9d211a1f2fa.

This commit was causing issue with diagnostics:
https://zed-industries.slack.com/archives/C07NUKHLVUZ/p1767999287421729

Release Notes:

- Reverted #46437
f5c924c583Marshall Bowers committed on 1/9/2026, 11:21:48 PM· committed by GitHubparentdffed22
2 files changedLine totals unavailable