xds: Reject duplicate endpoint addresses in EDS

[valeter]

Fixes #13119.

Reject duplicate endpoint socket addresses while parsing EDS resources.
Previously, these resources were ACKed and could trigger a panic in
outlier detection.

Track addresses across the original locality entries, including entries
that may later be overwritten in the locality-keyed output map. Reject
duplicates via ResourceInvalidException so the existing NACK path retains
the last accepted resource and version.

Validation includes additional addresses when dual-stack is enabled.
The same IP with different ports remains valid, and zero-weight
localities remain ignored.

Regression tests cover duplicates within and across localities and
priorities, overwritten locality entries, equivalent IPv6 addresses,
dual-stack addresses, cold start, repeated NACKs, and recovery.

Testing

• Original parser: 14 of 18 new parameterized regression cases fail.
• Patched parser: all 272 cases in GrpcXdsClientImplV3Test pass using
  a standalone JUnit harness with grpc-java 1.85.0 dependencies.
• Checkstyle 10.26.1 passes for both modified files.

Gradle build success

[16:17:13] /Users/valter/projects/grpc-java-pr git:(fix-13119-duplicate-eds-endpoints) > ./gradlew -PskipCodegen=true -PskipAndroid=true \
    :grpc-xds:test --tests io.grpc.xds.GrpcXdsClientImplV3Test \
    :grpc-xds:checkstyleMain :grpc-xds:checkstyleTest

Welcome to Gradle 8.14.5!

Here are the highlights of this release:
 - Java 24 support
 - GraalVM Native Image toolchain selection
 - Enhancements to test reporting
 - Build Authoring improvements

For more details see https://docs.gradle.org/8.14.5/release-notes.html

Starting a Gradle Daemon (subsequent builds will be faster)
*** Skipping the build of codegen and compilation of proto files because skipCodegen=true
  * Skipping the build of Android projects because skipAndroid=true

> Task :grpc-services:compileJava
Note: Some input files use or override a deprecated API.
Note: Recompile with -Xlint:deprecation for details.

[Incubating] Problems report is available at: file:///Users/valter/projects/grpc-java-pr/build/reports/problems/problems-report.html

Deprecated Gradle features were used in this build, making it incompatible with Gradle 9.0.

You can use '--warning-mode all' to show the individual deprecation warnings and determine if they come from your own scripts or plugins.

For more on this, please refer to https://docs.gradle.org/8.14.5/userguide/command_line_interface.html#sec:command_line_warnings in the Gradle documentation.

BUILD SUCCESSFUL in 3m 9s
83 actionable tasks: 83 executed

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: valeter / name: Ivan Anisimov (f33829e)