[Feature] add Mooncake Store

[propanone1006]

Purpose

This PR integrates support for Mooncake Store as a unified cache backend in unified-cache-management.

It introduces a new UcmMooncakeStore connector that wraps MooncakeDistributedStore, enabling seamless dump/load/lookup operations for KV cache tensors in vLLM and related systems.

This provides:

• Improved extensibility for distributed cache offloading
• Full async event loop support and task scheduling
• Compatibility with safetensors-based serialization
• A consistent interface aligned with UcmKVStoreBase

Modifications

This PR adds the following files:

• unifiedcache/ucm_connector/ucm_mooncake.py: Mooncake connector implementation
• test/test_mooncake.py: Unit tests for dump/load/lookup logic
• test/mooncake.json: Example config file for testing

User-Facing Changes

✅ Yes. This PR introduces a new backend interface UcmMooncakeStore, which can now be selected for external KV cache operations.

No breaking changes to existing APIs.

Test

This patch was tested via:

• ✅ Unit tests in test/test_mooncake.py:
  • test_lookup_not_found
  • test_lookup_found
  • test_dump_once
  • test_dump_repeated
  • test_load_existing_data
  • test_load_non_existent_data