feat: add cbv.maxSteps option to control step limit

[wkrozowski]

This PR adds a set_option cbv.maxSteps N option that controls the maximum
number of simplification steps the cbv tactic performs. Previously the limit
was hardcoded to the Sym.Simp.Config default of 100,000 with no way for
users to override it. The option is threaded through cbvCore, cbvEntry,
cbvGoal, and cbvDecideGoal.

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[mathlib-lean-pr-testing]

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[leanprover-bot]

Reference manual CI status:

• ❗ Reference manual CI can not be attempted yet, as the nightly-testing-2026-03-04 tag does not exist there yet. We will retry when you push more commits. If you rebase your branch onto nightly-with-manual, reference manual CI should run now. You can force reference manual CI using the force-manual-ci label. (2026-03-04 13:37:41)
• ❗ Reference manual CI will not be attempted unless your PR branches off the nightly-with-manual branch. Try git rebase 551086c85480eb69b85b7a59de8e75208c74984a --onto cda84702e9b31165f1f83c657b532f36f34e0bd0. You can force reference manual CI using the force-manual-ci label. (2026-03-04 16:08:32)