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.cpp

@@ -1,6 +1,7 @@
 #include "Epub.h"
 
 #include <HardwareSerial.h>
+#include <JpegToBmpConverter.h>
 #include <SD.h>
 #include <ZipFile.h>
 
@@ -218,7 +219,45 @@ const std::string& Epub::getPath() const { return filepath; }
 
 const std::string& Epub::getTitle() const { return title; }
 
-const std::string& Epub::getCoverImageItem() const { return coverImageItem; }
+std::string Epub::getCoverBmpPath() const { return cachePath + "/cover.bmp"; }
+
+bool Epub::generateCoverBmp() const {
+  // Already generated, return true
+  if (SD.exists(getCoverBmpPath().c_str())) {
+    return true;
+  }
+
+  if (coverImageItem.empty()) {
+    Serial.printf("[%lu] [EBP] No known cover image\n", millis());
+    return false;
+  }
+
+  if (coverImageItem.substr(coverImageItem.length() - 4) == ".jpg" ||
+      coverImageItem.substr(coverImageItem.length() - 5) == ".jpeg") {
+    Serial.printf("[%lu] [EBP] Generating BMP from JPG cover image\n", millis());
+    File coverJpg = SD.open((getCachePath() + "/.cover.jpg").c_str(), FILE_WRITE, true);
+    readItemContentsToStream(coverImageItem, coverJpg, 1024);
+    coverJpg.close();
+
+    coverJpg = SD.open((getCachePath() + "/.cover.jpg").c_str(), FILE_READ);
+    File coverBmp = SD.open(getCoverBmpPath().c_str(), FILE_WRITE, true);
+    const bool success = JpegToBmpConverter::jpegFileToBmpStream(coverJpg, coverBmp);
+    coverJpg.close();
+    coverBmp.close();
+    SD.remove((getCachePath() + "/.cover.jpg").c_str());
+
+    if (!success) {
+      Serial.printf("[%lu] [EBP] Failed to generate BMP from JPG cover image\n", millis());
+      SD.remove(getCoverBmpPath().c_str());
+    }
+    Serial.printf("[%lu] [EBP] Generated BMP from JPG cover image, success: %s\n", millis(), success ? "yes" : "no");
+    return success;
+  } else {
+    Serial.printf("[%lu] [EBP] Cover image is not a JPG, skipping\n", millis());
+  }
+
+  return false;
+}
 
 std::string normalisePath(const std::string& path) {
   std::vector<std::string> components;

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;