[Feature]: Upgrade Plan for UCM Integration with SGLang

[pyxyzc]

🚀 The feature, motivation and pitch

Motivation

The current UCM integration with SGLang still depends on a version-specific patch originally built for SGLang 0.5.5 (sglang-adapt.patch). This makes it hard to keep up with the latest main branch and adds unnecessary friction for users.

We want to move to a patch-free integration model for SGLang:

• use UCM as a HiCache L3 storage backend on the latest SGLang main
• avoid modifying any SGLang source code
• make the integration available by installing UCM only

Ongoing Work

Todo PR:

PR1 (code): #886

• Add a UCM-side UnifiedCacheStore implementation for SGLang HiCache L3
• Use the SGLang dynamic backend to register unifiedcache
• Make the integration auto-activate after installing UCM

PR2 (docs): #891

• Update the SGLang quickstart to describe the new patch-free workflow
• Add new launch examples
• Update the SGLang Dockerfile

Alternatives

No response

Additional context

No response

[pyxyzc]

@ygwpz @nrj868