chore: CI: re-enable fsanitize job

[Kha]

Given its run time of >2hrs, the job is added as a secondary job for nightly releases and a primary job for full releases. A new check level for differentiating between nightlies and full releases is added for this.

(Trying to) reactivate lsan will happen in a follow-up PR.

[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 75342961fcc7bbcc911ad0497d18d95b0f008de9 --onto 5a4226f2bdcc6299df76285b1d30f238546c09fe. You can force Mathlib CI using the force-mathlib-ci label. (2025-11-19 16:23:38)
• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase 0471319b5add780028aaf26a52e9b75985a813b0 --onto 5306a3469d20caa5f9d80384a5c1effdb14e9c67. You can force Mathlib CI using the force-mathlib-ci label. (2025-11-21 19:29:15)

[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 75342961fcc7bbcc911ad0497d18d95b0f008de9 --onto d3dda9f6d4428a906c096067ecb75e432afc4615. You can force reference manual CI using the force-manual-ci label. (2025-11-19 16:23:40)
• ❗ Reference manual CI will not be attempted unless your PR branches off the nightly-with-manual branch. Try git rebase 0471319b5add780028aaf26a52e9b75985a813b0 --onto d3dda9f6d4428a906c096067ecb75e432afc4615. You can force reference manual CI using the force-manual-ci label. (2025-11-21 19:29:17)