fix: Fixed Image Sizing When No Width is Set (#1002)

## Summary

* **What is the goal of this PR?** (e.g., Implements the new feature for
file uploading.)
When no width is set for an image, the image currently automatically
sets to the width of the page. However, with this fix, the parser will
use the height and aspect ratio of the image to properly set a height
for it. See below example:


Before:

![IMG_8862](https://github.com/user-attachments/assets/64b3b92f-1165-45ca-8bdb-8e69613d9725)

After:

![IMG_8863](https://github.com/user-attachments/assets/5cb99b12-d150-4b37-ae4c-c8a20eb9f3a0)


* **What changes are included?✱
Changes to the CSS parser

## Additional Context

* Add any other information that might be helpful for the reviewer
(e.g., performance implications, potential risks,
  specific areas to focus on).

---

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lib/Epub/Epub/css/CssParser.h

@@ -30,6 +30,9 @@
  */
 class CssParser {
  public:
+  // Bump when CSS cache format or rules change; section caches are invalidated when this changes
+  static constexpr uint8_t CSS_CACHE_VERSION = 3;
+
   explicit CssParser(std::string cachePath) : cachePath(std::move(cachePath)) {}
   ~CssParser() = default;
 
@@ -113,6 +116,8 @@ class CssParser {
   static CssFontWeight interpretFontWeight(const std::string& val);
   static CssTextDecoration interpretDecoration(const std::string& val);
   static CssLength interpretLength(const std::string& val);
+  /** Returns true only when a numeric length was parsed (e.g. 2em, 50%). False for auto/inherit/initial. */
+  static bool tryInterpretLength(const std::string& val, CssLength& out);
 
   // String utilities
   static std::string normalized(const std::string& s);