perf: mark inhabited arguments to extern as borrowed

[hargoniX]

This PR marks the Inhabited arguments of all functions in core marked as extern as borrowed
(panicking array accessors and panic! itself). This in turn causes a transitive effect throughout
the codebase and promotes most, if not all, Inhabited arguments to functions to borrowed.

[hargoniX]

!bench

[leanprover-radar]

Benchmark results for 3f4bbe5 against 5054448 are in. Significant changes detected! @hargoniX

• ✅ build//instructions: -16.8G (-0.14%)

Large changes (1✅)

• ✅ compiled/qsort//instructions: -63.8M (-0.34%)

Medium changes (1✅)

• ✅ compiled/parser//instructions: -49.2M (-0.13%)

Small changes (8✅, 1🟥)

• ✅ build/module/Init.Data.Nat.ToString//instructions: -76.4M (-0.24%)
• ✅ build/module/Lean.Elab.Do.Legacy//instructions: -100.2M (-0.18%)
• ✅ build/module/Lean.Elab.DocString//instructions: -81.7M (-0.17%)
• ✅ build/module/Lean.Meta.Tactic.Grind.Types//instructions: -86.6M (-0.21%)
• ✅ build/module/Std.Data.DHashMap.RawLemmas//instructions: -268.5M (-0.18%)
• ✅ build/module/Std.Data.DTreeMap.Raw.Lemmas//instructions: -113.7M (-0.14%)
• 🟥 compiled/rbmap_checkpoint//instructions: +3.8M (+0.03%)
• ✅ elab/big_do//instructions: -36.0M (-0.15%)
• ✅ elab/bv_decide_realworld//wall-clock: -47ms (-3.92%)

[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 50544489a9634d6842c64deeb284e62fe6ae523c --onto e6df474dd9c3ad0e21771eaa808c53f66222216d. You can force Mathlib CI using the force-mathlib-ci label. (2026-03-24 11:30:31)

[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 50544489a9634d6842c64deeb284e62fe6ae523c --onto cfa8c5a036d6990635c6ec50b02d0e806995cec3. You can force reference manual CI using the force-manual-ci label. (2026-03-24 11:30:32)