perf: Replace std::list with std::vector in text layout (#1038)

## Summary

_Revision to @blindbat's #802. Description comes from the original PR._

- Replace `std::list` with `std::vector` for word storage in `TextBlock`
and `ParsedText`
- Use index-based access (`words[i]`) instead of iterator advancement
(`std::advance(it, n)`)
- Remove the separate `continuesVec` copy that was built from
`wordContinues` for O(1) access — now unnecessary since
`std::vector<bool>` already provides O(1) indexing

## Why

`std::list` allocates each node individually on the heap with 16 bytes
of prev/next pointer overhead per node. For text layout with many small
words, this means:
- Scattered heap allocations instead of contiguous memory
- Poor cache locality during iteration (each node can be anywhere in
memory)
- Per-node malloc/free overhead during construction and destruction

`std::vector` stores elements contiguously, giving better cache
performance during the tight rendering and layout loops. The
`extractLine` function also benefits: list splice was O(1) but required
maintaining three parallel iterators, while vector range construction
with move iterators is simpler and still efficient for the small
line-sized chunks involved.

## Files changed

- `lib/Epub/Epub/blocks/TextBlock.h` / `.cpp`
- `lib/Epub/Epub/ParsedText.h` / `.cpp`

## AI Usage

YES

## Test plan

- [ ] Open an EPUB with mixed formatting (bold, italic, underline) —
verify text renders correctly
- [ ] Open a book with justified text — verify word spacing is correct
- [ ] Open a book with hyphenation enabled — verify words break
correctly at hyphens
- [ ] Navigate through pages rapidly — verify no rendering glitches or
crashes
- [ ] Open a book with long paragraphs — verify text layout matches
pre-change behavior

---------

Co-authored-by: Kuanysh Bekkulov <kbekkulov@gmail.com>

lib/Epub/Epub/blocks/TextBlock.cpp

@@ -12,16 +12,13 @@ void TextBlock::render(const GfxRenderer& renderer, const int fontId, const int
     return;
   }
 
-  auto wordIt = words.begin();
-  auto wordStylesIt = wordStyles.begin();
-  auto wordXposIt = wordXpos.begin();
   for (size_t i = 0; i < words.size(); i++) {
-    const int wordX = *wordXposIt + x;
-    const EpdFontFamily::Style currentStyle = *wordStylesIt;
-    renderer.drawText(fontId, wordX, y, wordIt->c_str(), true, currentStyle);
+    const int wordX = wordXpos[i] + x;
+    const EpdFontFamily::Style currentStyle = wordStyles[i];
+    renderer.drawText(fontId, wordX, y, words[i].c_str(), true, currentStyle);
 
     if ((currentStyle & EpdFontFamily::UNDERLINE) != 0) {
-      const std::string& w = *wordIt;
+      const std::string& w = words[i];
       const int fullWordWidth = renderer.getTextWidth(fontId, w.c_str(), currentStyle);
       // y is the top of the text line; add ascender to reach baseline, then offset 2px below
       const int underlineY = y + renderer.getFontAscenderSize(fontId) + 2;
@@ -41,10 +38,6 @@ void TextBlock::render(const GfxRenderer& renderer, const int fontId, const int
 
       renderer.drawLine(startX, underlineY, startX + underlineWidth, underlineY, true);
     }
-
-    std::advance(wordIt, 1);
-    std::advance(wordStylesIt, 1);
-    std::advance(wordXposIt, 1);
   }
 }
 
@@ -80,15 +73,15 @@ bool TextBlock::serialize(FsFile& file) const {
 
 std::unique_ptr<TextBlock> TextBlock::deserialize(FsFile& file) {
   uint16_t wc;
-  std::list<std::string> words;
-  std::list<uint16_t> wordXpos;
-  std::list<EpdFontFamily::Style> wordStyles;
+  std::vector<std::string> words;
+  std::vector<uint16_t> wordXpos;
+  std::vector<EpdFontFamily::Style> wordStyles;
   BlockStyle blockStyle;
 
   // Word count
   serialization::readPod(file, wc);
 
-  // Sanity check: prevent allocation of unreasonably large lists (max 10000 words per block)
+  // Sanity check: prevent allocation of unreasonably large vectors (max 10000 words per block)
   if (wc > 10000) {
     LOG_ERR("TXB", "Deserialization failed: word count %u exceeds maximum", wc);
     return nullptr;

lib/Epub/Epub/blocks/TextBlock.h

@@ -2,9 +2,9 @@
 #include <EpdFontFamily.h>
 #include <HalStorage.h>
 
-#include <list>
 #include <memory>
 #include <string>
+#include <vector>
 
 #include "Block.h"
 #include "BlockStyle.h"
@@ -12,14 +12,14 @@
 // Represents a line of text on a page
 class TextBlock final : public Block {
  private:
-  std::list<std::string> words;
-  std::list<uint16_t> wordXpos;
-  std::list<EpdFontFamily::Style> wordStyles;
+  std::vector<std::string> words;
+  std::vector<uint16_t> wordXpos;
+  std::vector<EpdFontFamily::Style> wordStyles;
   BlockStyle blockStyle;
 
  public:
-  explicit TextBlock(std::list<std::string> words, std::list<uint16_t> word_xpos,
-                     std::list<EpdFontFamily::Style> word_styles, const BlockStyle& blockStyle = BlockStyle())
+  explicit TextBlock(std::vector<std::string> words, std::vector<uint16_t> word_xpos,
+                     std::vector<EpdFontFamily::Style> word_styles, const BlockStyle& blockStyle = BlockStyle())
       : words(std::move(words)),
         wordXpos(std::move(word_xpos)),
         wordStyles(std::move(word_styles)),