perf: tune Array.push runtime code

[hargoniX]

The current condition for the shared branch fires too often.

[hargoniX]

!bench

[leanprover-community-bot]

Mathlib CI status (docs):

• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase 844e82e176f497798de42973c14f65856bad45be --onto fe45ddd6105078a0a3bd855e5d94673e794f6b88. (2024-12-29 11:33:39)

[leanprover-bot]

Here are the benchmark results for commit 6790707.
There were significant changes against commit 844e82e:

  Benchmark             Metric                  Change
  ==============================================================
+ binarytrees           task-clock               -3.7% (-12.6 σ)
+ bv_decide_realworld   task-clock               -1.9% (-49.2 σ)
+ const_fold            task-clock               -3.3% (-11.3 σ)
+ const_fold            wall-clock               -3.3% (-11.1 σ)
+ simp_arith1           wall-clock               -3.8% (-32.1 σ)
+ stdlib                attribute application    -1.4% (-28.9 σ)
- stdlib                dsimp                     1.4% (925.1 σ)

[hargoniX]

!bench

[leanprover-bot]

Here are the benchmark results for commit 0cd8829.
There were significant changes against commit 844e82e:

  Benchmark   Metric          Change
  ============================================
+ big_do      branch-misses    -8.1% (-43.7 σ)
+ big_do      maxrss           -1.1% (-17.5 σ)