Refactor metadata and internal data structures

Replace Metadata.h with Containers.h, introducing a HashTable
implementation with SIMD acceleration and specialized track tracking.
Cleanup PlayerEngine logic by merging it into the playback flow and
refactoring several internal API signatures.

include/File.h

@@ -1,22 +1,22 @@
 #pragma once
 
+#include "Containers.h"
+
 #include <filesystem>
 #include <vector>
 #include <string>
-#define MUSIC_FOLDER = {"data/"};
 
 namespace fs = std::filesystem;
 
 class File {
     public:
         void importFile( std::string fileName );
-        void importFolder( std::string folderPath );
-        std::vector<std::string> filenames_;
+        void importFolder( const std::string& folderPath, std::vector<Track>& tracks );
+        void readFileTag( const char* fileName );
+        std::string parseFiletype( const std::string& path );
+
     private:
         std::string path_;
-        fs::path musicFolder_ MUSIC_FOLDER;
+        fs::path musicFolder_ = "data/";
         std::string fileName_;
-        fs::path fp_ = musicFolder_ / fileName_;
 };
-
-    std::string_view parseFiletype( std::string_view path );