Book cover sleep screen (#89)

## Summary

* Fix issue with 2-bit bmp rendering
* Add support generate book cover BMP from JPG and use as sleep screen

## Additional Context

* It does not support other image formats beyond JPG at this point
* Something is cooked with my JpegToBmpConverter logic, it generates
weird interlaced looking images for some JPGs

| Book 1 | Book 2|
| --- | --- |
|
![IMG_5653](https://github.com/user-attachments/assets/49bbaeaa-b171-44c7-a68d-14cbe42aef03)
|
![IMG_5652](https://github.com/user-attachments/assets/7db88d70-e09a-49b0-a9a0-4cc729b4ca0c)
|

lib/Epub/Epub.h

@@ -48,7 +48,8 @@ class Epub {
   const std::string& getCachePath() const;
   const std::string& getPath() const;
   const std::string& getTitle() const;
-  const std::string& getCoverImageItem() const;
+  std::string getCoverBmpPath() const;
+  bool generateCoverBmp() const;
   uint8_t* readItemContentsToBytes(const std::string& itemHref, size_t* size = nullptr,
                                    bool trailingNullByte = false) const;
   bool readItemContentsToStream(const std::string& itemHref, Print& out, size_t chunkSize) const;