Deduplicate identical CSS files in EPUB parsing & probe images for dimensions instead of reading the full file

Some EPUB converters emit byte-identical stylesheets per chapter (100+ entries). Now scan the ZIP central directory once to identify duplicates by CRC32 and compressed size, then skip parsing identical files. This avoids redundant ZIP lookups and SD extraction round-trips while preserving all styles since rules merge into a global set. Also add extractItemToFile helper and allowEarlyStop parameter to readItemContentsToStream.

lib/ZipFile/ZipFile.h

@@ -69,7 +69,10 @@ class ZipFile {
   // Due to the memory required to run each of these, it is recommended to not preopen the zip file for multiple
   // These functions will open and close the zip as needed
   uint8_t* readFileToMemory(const char* filename, size_t* size = nullptr, bool trailingNullByte = false);
-  bool readFileToStream(const char* filename, Print& out, size_t chunkSize);
+  // allowEarlyStop: a short write from `out` is treated as the sink asking to
+  // stop (returns true) instead of a write failure — used by header probes
+  // that only need the first bytes of an entry.
+  bool readFileToStream(const char* filename, Print& out, size_t chunkSize, bool allowEarlyStop = false);
 
   template <typename F>
   bool enumerateFilePaths(F&& callback) {
@@ -80,6 +83,14 @@ class ZipFile {
       return true;
     }
 
+    return enumerateFileEntries([&callback](std::string_view path, uint32_t, uint32_t) { callback(path); });
+  }
+
+  // Callback receives (path, crc32, compressedSize) for each central-directory
+  // entry. Always scans the central directory: the slim-stat cache does not
+  // hold CRCs.
+  template <typename F>
+  bool enumerateFileEntries(F&& callback) {
     const bool wasOpen = isOpen();
     if (!wasOpen && !open()) {
       return false;
@@ -103,7 +114,11 @@ class ZipFile {
         break;
       }
 
-      file.seekCur(24);
+      file.seekCur(12);
+      uint32_t crc32, compressedSize;
+      file.read(&crc32, 4);
+      file.read(&compressedSize, 4);
+      file.seekCur(4);
       uint16_t nameLen, m, k;
       file.read(&nameLen, 2);
       file.read(&m, 2);
@@ -113,7 +128,7 @@ class ZipFile {
       if (nameLen < sizeof(itemName)) {
         file.read(itemName, nameLen);
         itemName[nameLen] = '\0';
-        callback(std::string_view{itemName, nameLen});
+        callback(std::string_view{itemName, nameLen}, crc32, compressedSize);
       } else {
         file.seekCur(nameLen);
       }