fix: add checkInterrupted to Core.withIncRecDepth

[nomeata]

This PR adds a checkInterrupted call to Core.withIncRecDepth, so that all recursive CoreM-based operations (inferType, whnf, isDefEq, simp, …) check for cancellation on each recursion step. Previously, these operations could run for seconds without responding to IDE cancellation requests.

This is the single highest-impact change for IDE cancellation responsiveness. It covers all recursive MetaM/TacticM operations at once, eliminating the vast majority of multi-second gaps identified by the LEAN_CHECK_SYSTEM_INTERVAL_MS monitoring in #13212.

Gap measurements pending — will be added after CI benchmarks and instrumented measurement.

Co-Authored-By: Claude Opus 4.6 noreply@anthropic.com

[nomeata]

!radar

[leanprover-radar]

Benchmark results for 4d782a6 against c4a664e are in. There are no significant changes. @nomeata

• 🟥 build//instructions: +2.2G (+0.02%)

Small changes (8🟥)

• 🟥 build/module/Lean.Compiler.LCNF.ToDecl//instructions: +19.0M (+0.47%)
• 🟥 build/module/Lean.Elab.PreDefinition.Structural.Preprocess//instructions: +19.7M (+1.69%)
• 🟥 build/module/Lean.Elab.PreDefinition.WF.FloatRecApp//instructions: +20.3M (+1.86%)
• 🟥 build/module/Lean.Meta.PProdN//instructions: +24.1M (+0.91%)
• 🟥 build/module/Lean.Meta.Reduce//instructions: +17.8M (+1.22%)
• 🟥 build/module/Lean.Meta.Tactic.Delta//instructions: +20.1M (+1.60%)
• 🟥 build/module/Lean.Meta.Tactic.Grind.MatchDiscrOnly//instructions: +21.2M (+1.30%)
• 🟥 build/module/Lean.Meta.Tactic.Grind.Util//instructions: +36.2M (+0.88%)

[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 c4a664eb5db2648780fa3c7a4be6d439e7233a72 --onto fc0cf68539ad3b481a1802414c22c44506519c9d. You can force Mathlib CI using the force-mathlib-ci label. (2026-04-06 15:14:10)

[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 c4a664eb5db2648780fa3c7a4be6d439e7233a72 --onto 861bc19e0c1c45b5766cc5c9ef0488568368b236. You can force reference manual CI using the force-manual-ci label. (2026-04-06 15:14:11)