fix: lake: properly prepend job log in ensureJob

[tydeu]

This PR ensures the the log error position is properly preserved when prepending stray log entries to the job log. It also adds comparison support for Log.Pos.

[leanprover-community-bot]

Mathlib CI status (docs):

• ❗ Batteries CI can not be attempted yet, as the nightly-testing-2024-11-30 tag does not exist there yet. We will retry when you push more commits. If you rebase your branch onto nightly-with-mathlib, Batteries CI should run now. (2024-12-02 22:26:15)
• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase d9d54c1f99363f42d1485f6b67f281a5985f684e --onto 3c5e612dc54733cd707becb929457d2f9d8ca6fd. (2024-12-02 23:41:13)