Add ConcurrentMap spliterator checks

[holly-agyei]

Adds ConcurrentMap-specific testlib coverage for derived keySet and entrySet spliterators, and updates LocalCache to satisfy it in both the JRE and Android source trees.

Fixes #7855

Implementation:

• add a new ConcurrentMapSpliteratorTester that checks keySet() and entrySet() spliterators report CONCURRENT and do not report SIZED
• wire that tester into ConcurrentMapTestSuiteBuilder so ConcurrentMap suites pick it up automatically
• add a focused ConcurrentMapTestSuiteBuilder self-test that verifies both the passing and failing cases
• override LocalCache derived-set spliterators in both JRE and Android variants to use concurrent unknown-size spliterators

Process:

• read and followed the repository guidance and matched the surrounding testlib and cache code style
• kept the scope to the issue and added regression coverage for the new behavior

Validation:

• direct junit.textui.TestRunner execution of com.google.common.collect.testing.ConcurrentMapTestSuiteBuilderTest passed
• direct javac compilation of the changed testlib and LocalCache sources passed
• full Maven test execution was not possible in this environment because Maven project loading failed on unresolved build extensions during local verification

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[holly-agyei]

CI fix: the earlier run failed because the spliterator() override added to android/guava/src/com/google/common/cache/LocalCache.java referenced java.util.Spliterator / Spliterators.spliteratorUnknownSize(...), which Animal Sniffer flagged against the Android API 23 signature (gummy-bears-api-23).

Pushed a follow-up commit (bcd722f) that annotates the new method with the package-local @IgnoreJRERequirement, following the convention already used for spliterator() in android/guava/src/com/google/common/collect/ImmutableCollection.java and primitive array wrappers. The main guava/src variant is unchanged because it's checked against the java18 signature, which includes Spliterator.

Verified locally:

• ./mvnw animal-sniffer:check -pl guava -f android/pom.xml — BUILD SUCCESS
• ./mvnw install -DskipTests=true -f android/pom.xml — BUILD SUCCESS (all 5 reactor modules)
• ./mvnw -pl guava-tests test -Dtest='LocalCacheTest,CacheBuilderSpecTest,CacheLoadingTest' -f android/pom.xml — 8,139 tests pass
• ./mvnw -pl guava-tests test -Dtest='LocalCacheTest,CacheBuilderSpecTest,CacheLoadingTest,ConcurrentMapTestSuiteBuilderTest,ConcurrentHashMultisetTest,MapMakerInternalMapTest' (main variant) — 13,998 tests pass

[cgdecker]

I think LocalCache.Values (which extends AbstractCollection) should also have its spliterator() implementation changed in a similar way (CONCURRENT and NONNULL).

[cgdecker]

This @author tag shouldn't be here. Besides being inaccurate here, we don't use @author tags at all anymore in new code.

[holly-agyei]

@cgdecker, thanks for the catch. Both fixed in d9e665d.

On the @author tag: I had copied the file header from a sibling tester (MapSpliteratorTester) as a starting point and missed removing the @author Louis Wasserman line. Sorry about that. I Dropped the tag entirely since new Guava code doesn't use them anymore.

[holly-agyei]

@cgdecker, thanks for the catch. Both fixed in d9e665d.

On the https://github.com/author tag: I had copied the file header from a sibling tester (MapSpliteratorTester) as a starting point and missed removing the https://github.com/author Louis Wasserman line. Sorry about that. I Dropped the tag entirely since new Guava code doesn't use them anymore.