feat: add cbv simprocs for arrays

[wkrozowski]

This PR adds cbv simprocs for getting elements out of arrays.

[wkrozowski]

!bench

[leanprover-radar]

Benchmark results for 031bae0 against b626c6d are in. There are no significant changes. @wkrozowski

• 🟥 build//instructions: +1.5G (+0.01%)

Small changes (2🟥)

• 🟥 lake/inundation/env//task-clock: +8ms (+5.60%)
• 🟥 lake/inundation/env//wall-clock: +9ms (+5.42%)

[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 b626c6d326043613ba296ef9869c19148c4f4297 --onto e8048291010c815d0d30926924e7ad7afc18b1c0. You can force Mathlib CI using the force-mathlib-ci label. (2026-03-10 18:55:10)

[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 b626c6d326043613ba296ef9869c19148c4f4297 --onto a165292462a973c20d3cc8c8b23a3ac2334a2a4a. You can force reference manual CI using the force-manual-ci label. (2026-03-10 18:55:11)