Make Lists.transform() delegate spliterator() to the backing list.

[Divyansh151005]

Problem

Lists.transform() list views did not override spliterator(). They inherited AbstractList/AbstractSequentialList spliterators that iterate via indexed access or list iterators on the transformed view. For backing lists with special spliterator behavior (notably CopyOnWriteArrayList, whose spliterator snapshots the array), streaming over the transformed view could throw ConcurrentModificationException while the backing list was being modified concurrently.

Example from the issue:

var cow = new CopyOnWriteArrayList<Integer>();
// ... concurrent adds/clears in another thread ...
Lists.transform(cow, s -> s).stream().forEach(x -> {}); // CME

Fixes #8165

Solution

Override spliterator() on both TransformingRandomAccessList and TransformingSequentialList to delegate through CollectSpliterators.map(fromList.spliterator(), …), matching Collections2.transform and Iterables.transform.

Testing

$ export JAVA_HOME=~/.m2/jdks/jdk-26.0.2+10/Contents/Home
$ ./mvnw -B -Dtoolchain.skip test -Dmaven.javadoc.skip=true \
    -Dsurefire.toolchain.version=17 \
    '-Dtest=com.google.common.collect.ListsTest#testTransformSpliterator*' \
    -DfailIfNoTests=false -pl guava-tests -am

[INFO] Tests run: 6002, Failures: 0, Errors: 0, Skipped: 0
[INFO] BUILD SUCCESS

New tests verify characteristic delegation for random-access and sequential transforms, and that streaming over Lists.transform(copyOnWriteArrayList, …) does not throw while the backing list is mutated concurrently.

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