Replace std::list with std::vector for the words, wordStyles,
wordXpos, and wordContinues containers in TextBlock and ParsedText.
Vectors provide contiguous memory layout for better cache locality
and O(1) random access, eliminating per-node heap allocation and
the 16-byte prev/next pointer overhead of doubly-linked list nodes.
The indexed access also removes the need for a separate continuesVec
copy that was previously built from the list for O(1) layout access.
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