feat: implement CSS enumeration through OPF directory when missing from manifest (#2148)

lib/ZipFile/ZipFile.h

@@ -3,6 +3,7 @@
 
 #include <deque>
 #include <string>
+#include <string_view>
 #include <unordered_map>
 
 class ZipFile {
@@ -69,4 +70,11 @@ class ZipFile {
   // 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);
+
+  template <typename F>
+  void enumerateFilePaths(F&& callback) const {
+    for (const auto& entry : fileStatSlimCache) {
+      callback(std::string_view{entry.first});
+    }
+  }
 };