feat: add newDecls fields to Core.State and Command.State

[wkrozowski]

This PR adds newDecls fields to Core.State and Command.State, that is reseted every-time we elab a top-level command and is used to record newly added declarations to the environment. The primary goal of this change is to enable Lean.Linters to easily look-up newly added declarations and lint them.

[wkrozowski]

!bench

[leanprover-radar]

Benchmark results for efa5c8f against 793cd14 are in. (These commits have already been benchmarked in a previous command.) No significant results found. @wkrozowski

• 🟥 build//instructions: +3.1G (+0.03%)

Small changes (1✅, 4🟥)

• 🟥 build/module/Lean.AddDecl//instructions: +196.6M (+3.24%) (reduced significance based on *//lines)
• 🟥 build/module/Lean.CoreM//instructions: +74.4M (+0.96%)
• 🟥 build/module/Lean.Elab.Command//instructions: +108.3M (+0.75%)
• 🟥 build/module/Lean.Elab.MutualDef//instructions: +104.3M (+0.37%)
• ✅ elab/grind_ring_5//instructions: -17.2M (-0.20%)

[wkrozowski]

!bench

[leanprover-radar]

Benchmark results for efa5c8f against 793cd14 are in. (These commits have already been benchmarked in a previous command.) No significant results found. @wkrozowski

• 🟥 build//instructions: +3.1G (+0.03%)

Small changes (1✅, 4🟥)

• 🟥 build/module/Lean.AddDecl//instructions: +196.6M (+3.24%) (reduced significance based on *//lines)
• 🟥 build/module/Lean.CoreM//instructions: +74.4M (+0.96%)
• 🟥 build/module/Lean.Elab.Command//instructions: +108.3M (+0.75%)
• 🟥 build/module/Lean.Elab.MutualDef//instructions: +104.3M (+0.37%)
• ✅ elab/grind_ring_5//instructions: -17.2M (-0.20%)

[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 793cd14b3816dfec686daa8515d6fc750c6f7326 --onto 803553a556fd82fa1060efb0c43eda542130cb16. You can force Mathlib CI using the force-mathlib-ci label. (2026-05-14 13:25:41)

[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 793cd14b3816dfec686daa8515d6fc750c6f7326 --onto 803553a556fd82fa1060efb0c43eda542130cb16. You can force reference manual CI using the force-manual-ci label. (2026-05-14 13:25:43)

[nomeata]

Does this work as expected in the presence of asynchronous elaboration? It seems this currently ignores declarations added asynchronously, but should it may block on that?