test: align v0.28.1 runtime contracts

[alexanderbin123]

Summary

• Align the LightOp boundary audit with two already-merged non-public imports using exact owner/module/symbol exceptions, while requiring the exception inventory to match production and rejecting use elsewhere.
• Update CPU-only DeepGEMM tests to fake the current DeepGEMM INT8 entry points, assert the DeepGEMM → LightOp activation → DeepGEMM sequence, and fail if routing regresses to the former LightOp GEMM APIs.
• Bring the local Scheduler test double in line with the pinned vLLM 0.28.1 _update_after_schedule interface.
• Change tests only; no vllm_hcu/ runtime or development functionality is modified.

Validation

• Baseline affected set: 5 failed, 24 passed.
• Updated affected set: 30 passed.
• Full portable contract against frozen vLLM SHA 58ad1f3b8973b23943107b51230d594050b42ec3: 1569 passed, 145 deselected.
• Inventory suite: 81 passed.
• Patch coverage audit: clean (110 adapters, no missing or untested modules).
• Production boundary audit: clean (275 Python files).
• compileall, git diff --check, test-only diff check, and credential scan: clean.

Scope

The two LightOp imports are grandfathered only at their current exact locations. This MR does not claim that those APIs are public or change their runtime behavior.