test: move cbv tests to appropriate directories

[wkrozowski]

This PR moves cbv tests to the correct test directories. cbv4.lean is a
straightforward elaboration test and is moved to tests/elab/. The AES and ARM
load/store tests are performance-oriented stress tests and are moved to
tests/elab_bench/.

[wkrozowski]

!bench

[leanprover-radar]

Benchmark results for aa2753a against 551086c are in! @wkrozowski

• 🟥 build//instructions: +760.2M (+0.01%)

No significant changes detected.

[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 551086c85480eb69b85b7a59de8e75208c74984a --onto cda84702e9b31165f1f83c657b532f36f34e0bd0. You can force Mathlib CI using the force-mathlib-ci label. (2026-03-04 16:30:07)

[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 551086c85480eb69b85b7a59de8e75208c74984a --onto cda84702e9b31165f1f83c657b532f36f34e0bd0. You can force reference manual CI using the force-manual-ci label. (2026-03-04 16:30:09)