[Feature] Refactor Registry Implement

[Stellar1999]

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Apache Dubbo Component

Java SDK (apache/dubbo)

Descriptions

1. When the Registry is wrapped and created by ListenerRegistryWrapper, there is a possibility that the Registry is null (due to connection failure), which may result in a NullPointerException (NPE) in subsequent operations.
   Should we consider handling this error during initialization? If the Registry is null, an error can be thrown, allowing the upper-layer caller to handle it accordingly.

2. When obtaining the ProviderUrl and the registration mode is ALL (default value), a ServiceDiscoveryRegistry URL will be generated synchronously (org.apache.dubbo.config.utils.ConfigValidationUtils#genCompatibleRegistries).
   However, if multiple registries exist and one of them goes down, the ServiceDiscoveryRegistry fails to generate, causing the startup process to fail.

   Should we consider:

   • 1. Implementing functionality in ServiceDiscoveryRegistry similar to MultipleRegistry, supporting check.
   • 2. Lowering the dependency level of ServiceDiscoveryRegistry, making it an attribute of Registry, and allowing other registries to handle its operations.

Related issues

#15003

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