chore: Elab.async benchmarking

[Kha]

Stacked on #6209

[Kha]

!bench

[leanprover-bot]

Here are the benchmark results for commit 13c79f9.
There were significant changes against commit 884a9ea:

  Benchmark             Metric                 Change
  =============================================================
- big_do                branches                 1.9%  (46.1 σ)
- big_do                instructions             1.8%  (41.1 σ)
- big_omega.lean        branch-misses            6.4%  (26.7 σ)
- big_omega.lean        branches                 1.7%  (96.3 σ)
- big_omega.lean        instructions             1.5%  (97.4 σ)
- bv_decide_mul         branch-misses            2.3%  (11.3 σ)
- bv_decide_realworld   branch-misses            1.3%  (10.5 σ)
+ import Lean           wall-clock              -4.3% (-10.2 σ)
+ lake env              task-clock              -9.3% (-13.2 σ)
+ lake env              wall-clock              -9.3% (-13.0 σ)
- simp_arith1           branch-misses            3.2%  (27.1 σ)
+ stdlib                instantiate metavars    -8.8% (-86.5 σ)

[leanprover-community-bot]

Mathlib CI status (docs):

• ✅ Mathlib branch lean-pr-testing-6210 has successfully built against this PR. (2024-11-25 13:59:23) View Log
• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase 88e3a2b1ab287020d5a393dc53c9441aa868681f --onto 9a17919ef11c2dba824498229633b8333a0b53d9. (2024-11-27 16:34:44)
• ✅ Mathlib branch lean-pr-testing-6210 has successfully built against this PR. (2024-11-28 14:50:44) View Log
• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase 86f303774a7fbf38406ae13bd4b66f2753643a45 --onto 6d495586a1836da3e12efb4fbf9946bd9088ac5f. (2024-11-29 16:23:48)