feat: add tracing to cbv

[wkrozowski]

This PR adds a basic tracing infrastructure to cbv tactic.

[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 47833725eaded4cec8cc7944ab656eaf05208da7 --onto e8048291010c815d0d30926924e7ad7afc18b1c0. You can force Mathlib CI using the force-mathlib-ci label. (2026-03-12 16:13:52)

[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 47833725eaded4cec8cc7944ab656eaf05208da7 --onto 24acf2b895670fdeeafc64c4f606e7a0ebc19e6d. You can force reference manual CI using the force-manual-ci label. (2026-03-12 16:13:54)

[wkrozowski]

!bench

[leanprover-radar]

Benchmark results for b70eb93 against 4783372 are in. There are no significant changes. @wkrozowski

• 🟥 build//instructions: +9.0G (+0.07%)

Small changes (4🟥)

• 🟥 build/module/Lean.Meta.Tactic.Cbv.CbvSimproc//instructions: +752.6M (+15.53%) (reduced significance based on *//lines)
• 🟥 build/module/Lean.Meta.Tactic.Cbv.ControlFlow//instructions: +661.5M (+10.42%) (reduced significance based on *//lines)
• 🟥 build/module/Lean.Meta.Tactic.Cbv.Main//instructions: +7.4G (+128.95%) (reduced significance based on *//lines)
• 🟥 build/module/Lean.Meta.Tactic.Cbv//instructions: +141.1M (+21.77%) (reduced significance based on *//lines)