chore: restoreAllArtifacts = true for core

[tydeu]

This PR sets restoreAllArtifacts = true in the core build Lake configuration file.

[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 5b8d4d72104e66de541339027b41b7e434c1ab7e --onto ac0b82933f6eac9914011ca2caf38d0e4e991160. You can force Mathlib CI using the force-mathlib-ci label. (2025-09-27 03:05:10)

[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 5b8d4d72104e66de541339027b41b7e434c1ab7e --onto d3dda9f6d4428a906c096067ecb75e432afc4615. You can force reference manual CI using the force-manual-ci label. (2025-09-27 03:05:11)