fix: language server dropping requests

[mhuisi]

This PR fixes a race condition in the language server that would sometimes cause it to drop requests and never respond to them when editing the header of a file. This in turn could cause semantic highlighting to stop functioning in VS Code, as VS Code would stop emitting requests when a prior request was dropped, and also cause the InfoView to become defective. It would also cause import auto-completion to feel a bit wonky, since these requests were sometimes dropped. This race condition has been present in the language server since its first version in 2020.

This PR also reverts the futile fix attempt in #7130.

The specific race condition was that if the file worker crashed or had to be restarted while a request was in flight in the file worker, then we wouldn't correctly replay it in our watchdog crash-restart logic. This PR adjusts this logic to fix this.

[leanprover-community-bot]

Mathlib CI status (docs):

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• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase ad1e04c82697938afb1df0525d8207dafaf8e043 --onto 2960b384af1f29f566f59a3ede8ac982e4628f19. (2025-02-23 20:15:55)