[PR] #15935 Enhance NetUtils IPv6 handling and test coverage

[krrishmahar]

What is the purpose of the change?

This PR addresses issue #15935 by improving IPv6-related test coverage in NetUtils.

Specifically, it:

• Adds unit tests for IPv6 address normalization without scope.
• Verifies IPv6 CIDR matching behavior in matchIpExpression.
• Ensures unsupported IPv6 wildcard patterns fail fast with clear exceptions.
• Validates mismatched IPv4 pattern and IPv6 host scenarios.
• Documents current implementation-defined behavior via tests, without modifying runtime logic.

No functional behavior is changed; this PR focuses on correctness, clarity, and maintainability through testing.

Brief changelog

• NetUtilsTest.java
  • Added IPv6 normalization tests.
  • Added IPv6 CIDR and invalid pattern matching tests.
  • Added validation for IPv4/IPv6 mismatch cases.
  • Documented unsupported IPv6 wildcard behavior.

Verifying this change

Validated locally by running:

mvn test -Dtest=NetUtilsTest -pl dubbo-common

And verify build by running:

./mvnw -e --batch-mode --no-snapshot-updates --no-transfer-progress --fail-fast clean install -Psources,skip-spotless,checkstyle -Dmaven.test.skip=true

Checklist

• Make sure there is a GitHub_issue field for the change.
• Write a pull request description that is detailed enough to understand what the pull request does, how, and why.
• Write necessary unit-test to verify behavior. No production logic is changed.
• Make sure GitHub Actions can pass.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 60.69%. Comparing base (56924bb) to head (ac4781f).

Additional details and impacted files

@@             Coverage Diff              @@
##                3.3   #15974      +/-   ##
============================================
- Coverage     60.69%   60.69%   -0.01%     
- Complexity    11706    11709       +3     
============================================
  Files          1946     1946              
  Lines         88701    88701              
  Branches      13374    13374              
============================================
- Hits          53838    53837       -1     
- Misses        29353    29354       +1     
  Partials       5510     5510              

Flag	Coverage Δ
integration-tests-java21	32.20% <ø> (-0.06%)	⬇️
integration-tests-java8	32.32% <ø> (-0.08%)	⬇️
samples-tests-java21	32.10% <ø> (-0.03%)	⬇️
samples-tests-java8	29.69% <ø> (+0.03%)	⬆️
unit-tests-java11	58.97% <ø> (-0.01%)	⬇️
unit-tests-java17	58.46% <ø> (-0.04%)	⬇️
unit-tests-java21	58.46% <ø> (-0.01%)	⬇️
unit-tests-java25	58.42% <ø> (-0.02%)	⬇️
unit-tests-java8	58.98% <ø> (-0.02%)	⬇️

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[RainYuY]

LGTM

[EarthChen]

LGTM