fix: add null-safety checks for labels and services in K8s RPC ingress parsers

[wy471x]

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• You submit test cases (unit or integration tests) that back your changes.
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Summary

Bug Fix (3 files)

DubboIngressParser.java, GrpcParser.java, SofaParser.java — in each parseIngressRule method, added null-safety guards before iterating over labels:

1. Null/empty labels check — if labels is null or empty, skip the label iteration with continue instead of throwing NullPointerException.
2. Missing service check — before calling .getMetadata().getAnnotations(), check if serviceLister.namespace(namespace).get(...) returned null (service not yet in cache). Log a
   warning and continue, allowing a later reconcile to pick it up once the service cache is populated.

Unit Tests (3 new files, 9 tests)

• DubboIngressParserTest.java — 3 tests
• GrpcParserTest.java — 3 tests
• SofaParserTest.java — 3 tests

close #6486