[FEATURES] Unified Cache Runtime Framework

[cheyang]

What feature you'd like to add: Design and implement standardized Cache Runtime interfaces for lifecycle management, cache I/O, metadata operations, flush/writeback, and metrics exposure. Deliver reference adapters as blueprints or PoCs for CubeFS, DragonFly, and similar engines, including compatibility layers for Alluxio, Vineyard, and JuiceFS.

Why is this feature needed: A universal Cache Runtime interface enables rapid integration of new engines with Fluid, making the platform more extensible and operator-friendly. Standard compatibility layers ensure seamless support for both existing and new engines, accelerating integration and testing for diverse data acceleration scenarios.