fix: Signal.Handler segmentation fault with Selector

[algebraic-dev]

This PR adds more event_loop_locks to fix race conditions.

[leanprover-community-bot]

Mathlib CI status (docs):

• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase f21f8d96f97989d3a34148329a158e94b220314b --onto 0708024c4649f11da1276d8b6d4345972a9dc57c. You can force Mathlib CI using the force-mathlib-ci label. (2025-12-18 00:57:45)

[leanprover-bot]

Reference manual CI status:

• ❗ Reference manual CI will not be attempted unless your PR branches off the nightly-with-manual branch. Try git rebase f21f8d96f97989d3a34148329a158e94b220314b --onto 0708024c4649f11da1276d8b6d4345972a9dc57c. You can force reference manual CI using the force-manual-ci label. (2025-12-18 00:57:47)