fix: Remove separations after style changes (#720)

Closes #182. Closes #710. Closes #711.

## Summary

**What is the goal of this PR?**
- A longer-term, more robust fix for the issue with spurious spaces
appearing after style changes. Replaces solution from #694.

**What changes are included?**
- Add continuation flags to determine if to add a space after a word or
if the word connects to the previous word. Replaces simple solution that
only considered ending punctuation.
- Fixed an issue with greedy line-breaking algorithm where punctuation
could appear on the next line, separated from the word, if there was a
style change between the word and punctuation

---

### AI Usage

While CrossPoint doesn't have restrictions on AI tools in contributing,
please be transparent about their usage as it
helps set the right context for reviewers.

Did you use AI tools to help write this code? _**YES**_, Claude Code

lib/Epub/Epub/parsers/ChapterHtmlSlimParser.h

@@ -30,6 +30,7 @@ class ChapterHtmlSlimParser {
   // leave one char at end for null pointer
   char partWordBuffer[MAX_WORD_SIZE + 1] = {};
   int partWordBufferIndex = 0;
+  bool nextWordContinues = false;  // true when next flushed word attaches to previous (inline element boundary)
   std::unique_ptr<ParsedText> currentTextBlock = nullptr;
   std::unique_ptr<Page> currentPage = nullptr;
   int16_t currentPageNextY = 0;