[CI]Add CI summary log (#7202)

### What this PR does / why we need it?
This PR adds a new CI log summarizer, `ci_log_summary.py`, and wires it
into unit-test and e2e workflows so failed jobs publish a structured
failure summary to the GitHub step summary.
Examples:
- `python3 .github/workflows/scripts/ci_log_summary.py --log-file
/tmp/unit-test.log --mode ut --step-name "Unit test"`
- `python3 .github/workflows/scripts/ci_log_summary.py --run-id
23127187822 --format json`

A maintenance note is added to `ci_utils.py` to clarify that the `START`
/ `PASSED` / `FAILED (exit code X)` log lines are parsed by
`ci_log_summary.py`, so any future format changes must be coordinated
with the corresponding summarizer regexes.

🤖 Generated with [Codex]<noreply@openai.com>
- vLLM version: v0.16.0
- vLLM main:
4034c3d32e
---------
Signed-off-by: Meihan-chen <jcccx.cmh@gmail.com>
Signed-off-by: meihanc <jcccx.cmh@gmail.com>
Co-authored-by: Codex <noreply@openai.com>

.github/workflows/_unit_test.yaml

@@ -71,8 +71,10 @@ jobs:
         env:
           VLLM_WORKER_MULTIPROC_METHOD: spawn
           TORCH_DEVICE_BACKEND_AUTOLOAD: 0
+        shell: bash
         run: |
           export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/usr/local/Ascend/ascend-toolkit/latest/x86_64-linux/devlib
+          set -o pipefail
           pytest -sv --cov --cov-report=xml:unittests-coverage.xml tests/ut \
             --ignore tests/ut/model_loader/netloader/test_netloader_elastic.py \
             --ignore tests/ut/kv_connector/test_remote_prefill_lifecycle.py \
@@ -81,7 +83,18 @@ jobs:
             --ignore tests/ut/kv_connector/test_mooncake_connector.py \
             --ignore tests/ut/worker/test_worker_v1.py \
             --ignore tests/ut/spec_decode/test_mtp_proposer.py \
-            --ignore tests/ut/kv_connector/test_mooncake_layerwise_connector.py
+            --ignore tests/ut/kv_connector/test_mooncake_layerwise_connector.py \
+            2>&1 | tee /tmp/unit-test.log
+          exit ${PIPESTATUS[0]}
+
+      - name: Summarize unit test failure
+        if: ${{ always() }}
+        run: |
+          python3 .github/workflows/scripts/ci_log_summary.py \
+            --mode ut \
+            --step-name "Run unit test" \
+            --log-file /tmp/unit-test.log \
+            --output "$GITHUB_STEP_SUMMARY"
 
       - name: Upload coverage to Codecov
         # only upload coverage when commits merged