[CI] Split Quantization job into three directory-based steps

[khluu]

Purpose

Part of the effort to get every CI job under ~30 minutes. The Quantization step is one of the 10 longest jobs in main CI: 57–67 min of test execution (timeout 75) in recent nightly full runs (83094, 83068).

This splits tests/quantization/ into subdirectories so each CI step runs a whole directory — no per-file lists in YAML, so a new test file is automatically covered by whichever step owns its directory (matching the existing convention of tests/models/language/{generation,pooling} and tests/kernels/{attention,moe,quantization}):

step	directory	measured test time (slow / fast night)
Quantization (Core)	core/ + package root sweep	22.3 / 17.8 min
Quantization (Compressed Tensors)	compressed_tensors/	21.6 / 17.9 min
Quantization (Checkpoint Formats)	checkpoint_formats/	23.5 / 21.1 min
Quantized MoE Test (B200) (existing)	blackwell/	unchanged

Times come from per-test timestamps extracted from the Buildkite logs of the two nightly builds (529 tests; per-file sums reconcile with pytest's reported totals to within 0.1 min). Each new step lands at ~28–30 min wall including image pull, with timeout_in_minutes: 45.

Design notes:

• The Core step runs pytest quantization/ --ignore the sibling directories, so any file at the package root (including future ones) is always collected by exactly one step. Platform-gated files (test_cpu_w8a8.py, test_cpu_wna16.py, test_gfx950_moe.py) stay at the root — they self-skip off-platform and are referenced by exact path from the CPU/AMD pipelines.
• test_blackwell_moe.py moves into blackwell/, so the old --ignore quantization/test_blackwell_moe.py disappears from the NVIDIA and AMD commands; the B200 step now runs the directory.
• The torchao/conch installs are kept on all three steps to avoid any kernel-selection behavior change; narrowing them per-step can be a follow-up.
• Moved files' relative imports were converted to absolute tests.* imports; all exact-path references were updated (AMD test-amd.yaml, Intel intel_jobs/*, CPU hardware_tests/cpu.yaml + run-cpu-test-arm.sh, test_areas/kernels.yaml DeepGEMM step, docs/features/quantization/modelopt.md).

Not a duplicate

Checked gh pr list for open PRs touching the Quantization CI job or tests/quantization structure (searches: "quantization test split", "test_areas quantization", CI breakdown) — no open PR addresses this.

Test plan

Config + file-move change; no runtime code touched, so no model evaluation is applicable. The test set is a pure re-partition: same files, same -k 'not test_compressed_tensors_w4a8_fp8' deselect (now scoped to the Compressed Tensors step, where that test lives), same blackwell exclusion semantics.

Ran locally:

• pre-commit on the commit — all hooks passed (ruff check/format, mypy 3.10, typos, shellcheck, SPDX headers)
• YAML parse of all six touched pipeline files
• python -m py_compile on all moved test files
• Repo-wide sweep for stale references to every moved filename — none remain

The three new steps in this PR's own CI run are the end-to-end validation that collection and imports resolve; reviewers can compare collected-test counts against the previous single job (485 passed / 46 skipped / 1 deselected in the nightlies).

AI assistance

This change was developed with AI assistance (Claude). Timing analysis was derived from nightly Buildkite logs; every changed line has been reviewed.

🤖 Generated with Claude Code

[claude]

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[mergify]

Documentation preview: https://vllm--51955.org.readthedocs.build/en/51955/

[khluu]

/ci run

[github-actions]

✅ Triggered Buildkite CI #83535 for commit 3c6f9a635a21.

[khluu]

Claude Code here (posting on behalf of @khluu) — CI verification results from build 83535:

The three new steps all passed, each under 25 min wall (vs 68 min for the old single job in the last nightly):

step	wall time	pytest result
Quantization (Core)	20.3 min	77 passed, 19 skipped
Quantization (Compressed Tensors)	24.5 min	280 passed, 1 deselected
Quantization (Checkpoint Formats)	24.2 min	134 passed, 27 skipped

No coverage lost: 491 passed / 46 skipped / 1 deselected total, vs 490 / 46 / 1 for the single job in the last nightly on main (build 83443). The +1 passed is a test added by #50074 after that nightly ran.

Other touched paths verified in this build:

• Quantized MoE Test (B200) ✅ — runs tests/quantization/blackwell directory
• Kernels DeepGEMM Test (H100) ✅ — runs moved quantization/checkpoint_formats/test_cutlass_w4a16.py
• CPU-Quantization Model Tests ✅ — runs moved compressed_tensors/test_compressed_tensors.py::test_compressed_tensors_w8a8_logprobs

Unrelated failure: Kernels Core Operation Test fails 3 precision assertions in tests/kernels/core/test_fused_quant_layernorm.py (untouched by this PR — the step ran only because kernels.yaml changed for the DeepGEMM path). The same step failed identically on main in nightly build 83443, so it's pre-existing main breakage, not introduced here.

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @khluu.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork