[v0.19.1rc1] fix(npu): preserve AFD DBO config during auto worker selection

[jiangkuaixue123]

Summary

• Preserve AFD-owned NPU DBO and ubatching settings during vLLM-Ascend config normalization.
• Keep upstream normalization unchanged for non-AFD configurations.
• Make the initial import-failure retry test deterministic under PEP 660 editable installs.

Root cause

vLLM-Ascend resets DBO-related fields while selecting and normalizing the NPU worker. AFD owns its NPU ubatching path and needs those values restored after upstream normalization. The retry test also removed vllm_ascend.platform from sys.modules, which still allowed an editable-install finder to reload the real module.

Validation

• python -m pytest tests/unit: 328 passed, 2 skipped.
• NPU E2E excluding async and accuracy: 14 passed, 4 expected DBO skips.
• DeepSeek-V3.2 8A4F Attention/FFN smoke request returned HTTP 200.

This PR includes the runtime changes from #190 plus the deterministic import-failure test fix.