Fix ComparableVector Comparable contract violation

[Copilot]

The ComparableVector class violated the Comparable contract: compareTo returned 0 on hash collisions even when vectors differed, while equals correctly compared array contents. This could cause data loss in TreeMap (used by TransactionIndexContext) where distinct vectors with matching hash codes would overwrite each other.

Changes

• LSMVectorIndex.ComparableVector.compareTo: Added lexicographical comparison fallback when hash codes collide
  • Fast path: compare hash codes first for performance
  • Collision path: element-by-element comparison, then length comparison
  • Ensures compareTo(v) == 0 ⟺ equals(v) == true

@Override
public int compareTo(final ComparableVector other) {
  // First compare by hash code for performance
  final int hashCompare = Integer.compare(this.hashCode, other.hashCode);
  if (hashCompare != 0)
    return hashCompare;
  
  // If hash codes are equal, perform lexicographical comparison of vector elements
  // to maintain the Comparable contract: compareTo == 0 iff equals == true
  final int minLength = Math.min(this.vector.length, other.vector.length);
  for (int i = 0; i < minLength; i++) {
    final int elementCompare = Float.compare(this.vector[i], other.vector[i]);
    if (elementCompare != 0)
      return elementCompare;
  }
  // If all compared elements are equal, compare by length
  return Integer.compare(this.vector.length, other.vector.length);
}

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