fix: make grind_lint see custom grind attrs

[raphael-solace]

This PR makes #grind_lint consider all registered grind attribute extensions instead of only the built-in @[grind] extension.

Custom grind sets created with register_grind_attr can now be skipped, muted, and included by lint checks, which is useful for downstream libraries that maintain specialized automation sets.

Closes #13733.

[raphael-solace]

changelog-tactics

[mathlib-lean-pr-testing]

Mathlib CI status (docs):

• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase 7f13a8988f0018f404d4bb0954f95122b8855084 --onto 2cd98639c40d2d2a026dd599093b70f55f55ffaf. You can force Mathlib CI using the force-mathlib-ci label. (2026-05-25 13:15:00)

[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 7f13a8988f0018f404d4bb0954f95122b8855084 --onto 803553a556fd82fa1060efb0c43eda542130cb16. You can force reference manual CI using the force-manual-ci label. (2026-05-25 13:15:03)