Lists.transform: Preserve spliterator characteristics from backing list

[nickita-khylkouski]

Summary

• Override spliterator() in TransformingSequentialList and TransformingRandomAccessList
• Delegate to backing list's spliterator via CollectSpliterators.map()
• Preserves characteristics: SIZED, SUBSIZED, ORDERED, IMMUTABLE, CONCURRENT

Motivation

Lists.transform() with CopyOnWriteArrayList throws ConcurrentModificationException during parallel stream operations because the default AbstractList.spliterator() doesn't inherit the IMMUTABLE characteristic from the backing list.

Before: Lists.transform(cowList, fn).parallelStream() → CME
After: Characteristics preserved, no CME

Implementation

Follows the exact pattern used in Collections2.TransformedCollection.spliterator():

@Override
@GwtIncompatible // Spliterator
public Spliterator<T> spliterator() {
  return CollectSpliterators.map(fromList.spliterator(), 0, function);
}

Testing

• ✅ ListsTest: 5,999 tests passed
• ✅ Collections2Test: 1,300 tests passed
• ✅ CollectSpliteratorsTest: 7 tests passed
• ✅ All transform-related tests: 548 tests passed
• ✅ Manual verification with CopyOnWriteArrayList concurrent stress test

Fixes #8165