[feat] support Kubernetes Gateway API

[eye-gu]

close #6346

Implements ShenYu support for Kubernetes Gateway API (gateway.networking.k8s.io/v1), complementing the existing Ingress support.

Core Components

Component	Description
GatewayClassReconciler	Watches GatewayClass, accepts those with spec.controllerName=shenyu
GatewayReconciler	Watches Gateway, re-queues affected HTTPRoutes on Gateway changes
HTTPRouteReconciler	Watches HTTPRoute, parses into ShenYu selector/rule via HttpRouteParser
HttpRouteParser	Translates HTTPRoute spec (hostnames + matches + backendRefs) into SelectorData/RuleData
GatewayRouteCache	Thread-safe cache for route↔selector and gateway↔route bindings
GatewayApiControllerConfiguration	Spring Boot auto-configuration for all Gateway API beans

Make sure that:

• You have read the contribution guidelines.
• You submit test cases (unit or integration tests) that back your changes.
• Your local test passed ./mvnw clean install -Dmaven.javadoc.skip=true.