feat(pipeline): support pipeline module in agentscope

**Background**

While implementing SOP support in AgentScope, we identified strong structural similarities between pipelines and SOPs — both require unified input interfaces, human-in-the-loop (HITL) handling, and orchestration of multi-agent operations. The key distinction is that pipelines operate on **fixed, predefined logic**, making them a natural and solid foundation for building SOPs.

**Changes**

- Introduce a `pipeline` module in AgentScope
- Support a variety of pipeline types

**Note**

Unlike AgentScope 1.0, the goal of this new pipeline module is to provide **more mature, well-encapsulated functionality**, rather than limiting it to simple primitives like `fanout` or `sequential`. We aim to cover richer, more practical orchestration patterns.

If you have proposals for new pipeline types or designs, feel free to open a discussion and submit a proposal — contributions and ideas are welcome!

No concrete files or tests are listed in the issue. Start by reading the existing SOP and orchestration-related codepaths and docs to infer how unified inputs, HITL, and multi-agent execution are currently modeled and exposed. Next, identify the module entry points where public functionality is registered so a new `pipeline` namespace can be added consistently, then run the relevant orchestration tests (or existing pipeline-equivalent tests) after any initial type implementation. Consider it done when a first cut of the pipeline module/API is integrated and documented enough to show clear behavior for one or more pipeline types.

Rédigé par le modèle d'indexation à partir du texte de l'issue.