[Feature] Refactor agent skills

[wangxingjun778]

Description

Refactor agent skills:

1. Easy to use, LLMAgent integration as a basic module
2. Improve context engineering for skills parsing, analysis and task planning.
3. Enhanced functionality with skill hub (on ModelScope hub)
4. Multi-platform support

[wangxingjun778]

Refer to PR: #845

Merged.

[wangxingjun778]

ms-agent v1.6.0rc0 released:

1. Release note: https://github.com/modelscope/ms-agent/releases/tag/v1.6.0rc0
2. PiPy： https://pypi.org/project/ms-agent/1.6.0rc0/