CI: stabilize Aiter wheel prebuilds

[gyohuangxin]

Summary

• Lower Aiter wheel prebuild concurrency from 128 to 64 via a workflow env knob.
• Capture prebuild logs and print a timing summary with runner, wall time, kernel count, and per-module compile costs.

Test plan

• python3 -m py_compile .github/scripts/aiter_prebuild_summary.py
• Parsed the workflow YAML successfully with PyYAML.
• Syntax-checked the generated build shell with bash -n.
• Ran git diff --check on the changed files.

[github-actions]

🏷️ CI Guide

Runs automatically on every PR:

• ✅ Pre-checks (submodule verification, code formatting)
• ✅ Aiter op tests (gfx942 + gfx950)
• ✅ Triton tests on MI35X (only when aiter/ops/triton/** or related paths are changed)

Extended tests (opt-in via labels):

Label	Tests
ci:triton-300x	Run an additional Triton test job on MI300X in PRs; main branch always runs both MI35X and MI300X
ci:sglang	SGLang integration tests: DeepSeek-R1-MXFP4 accuracy, Qwen 3.5 accuracy
ci:atom	ATOM benchmark: DeepSeek-R1-0528, GPT-OSS-120B
ci:atom_full	ATOM accuracy suite for PR and main models from ATOM models_accuracy.json
ci:vllm	vLLM benchmark: GPT-OSS-120B, DeepSeek-R1-0528, Kimi-K2.5
ci:all	All standard extended tests (excludes ci:atom_full)

Only add ci:atom_full for FlyDSL or Triton upgrades.
Add labels via the sidebar or gh pr edit 3126 --add-label <label>

[Copilot]

Pull request overview

This PR updates the Aiter CI wheel prebuild step to reduce build parallelism via a workflow-level knob and to emit a timing summary from the setup.py build logs, aiming to improve prebuild stability and observability in CI.

Changes:

• Introduces a workflow env knob (AITER_PREBUILD_MAX_JOBS) to reduce wheel build parallelism (MAX_JOBS) from 128 to 64.
• Captures setup.py output via tee and runs a new parser script to print a prebuild timing summary (runner, wall time, kernel count, and per-module compile costs).
• Adds .github/scripts/aiter_prebuild_summary.py to parse “finish build [...] cost ...” lines and report compilation timings.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
.github/workflows/aiter-test.yaml	Adds env knob for MAX_JOBS and runs a new summary pass over prebuild logs during wheel build.
.github/scripts/aiter_prebuild_summary.py	New helper script that parses prebuild logs to print a timing/kernel-count summary.

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