Pipeline Parallel for ktransformers for multi low-vram GPUs

### Reminder

- [x] I have read the above rules and searched the existing issues.

### Description

Looks like the pipeline parallel for sglang is not well implemented and we are a bit away from sglang main branch, I think we can use well-maintained vllm integrating with sglang parameter to have literal full control over this entire project.

### Pull Request

_No response_

No files, tests, or entry points are named. Start by locating the existing sglang pipeline-parallel implementation and the project’s vLLM integration, then clarify the supported multi-GPU configurations and acceptance criteria for pipeline parallelism on low-VRAM GPUs.

Written by the indexing model from the issue text.