Refactor the kvcache backend to support infinistore

[Jeffwan]

Pull Request Description

1. Remove centralized and distributed controller. Use KVBackendReconciler interface instead, each backend should implement their own reconciler
2. Build an abstract DistributedReconciler for both HPKV and Infinistore, they share most of the similar logic.
3. Build another KVBackend interface, they just provide objects and main reconcilation workflow is done by DistributedReconciler
4. Add enough use test coverage
5. Refactor some common helpers, constants to common libs.

Related Issues

Resolves: part of #948

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[Copilot]

Pull Request Overview

This PR refactors the kvcache backend to support infinistore by replacing the centralized/distributed controller with a KVBackendReconciler interface, building a common abstract DistributedReconciler for HPKV and Infinistore, and adding comprehensive test coverage and refactored common helpers.

• Removed centralized and distributed controller logic and replaced it with a per-backend reconciler design.
• Introduced a new DistributedReconciler, updated interfaces, and refactored helper functions and constants.
• Added extensive test cases for annotation processing, backend validation, and resource construction for each supported backend.

Reviewed Changes

Copilot reviewed 16 out of 16 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
pkg/utils/annotations.go & annotations_test.go	Added helper functions to extract annotations and tests verifying their correctness.
pkg/controller/kvcache/kvcache_controller.go	Refactored the controller logic to derive the backend dynamically and delegate reconciliation to backend-specific handlers.
pkg/controller/kvcache/backends/*	Introduced separate backend modules for Vineyard, HPKV, and Infinistore with their corresponding tests.
pkg/constants/kvcache.go	Updated constants to support the new backend names and refactored labeling conventions.
Other test files (e.g. infinistore_test.go, hpkv_test.go, distributed_test.go, common_test.go)	Added new test cases for validating the construction and reconciliation of backend-specific resources.

[Jeffwan]

I will merge this change to unblock another one. If someone has more feedback, please left comment here and I will address them in next PR