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/Tag.h

@@ -1,20 +1,26 @@
 #pragma once
 
-#include "Metadata.h"
+#include "containers.h"
+//#include "file.h"
+
+#include <filesystem>
 #include <memory>
 #include <taglib/tstring.h>
 #include <taglib/fileref.h>
 #include <taglib/tvariant.h>
 
 
-class Tag {
-    public:
-        void readTag( TagLib::FileName fileName );
-        Metadata getMetadata() const;
+namespace fs = std::filesystem;
 
-        const std::string& getFilePath() const;
-        const auto getArtwork() const;
+class tag {
+    public:
+        void readtag( TagLib::filename filename );
+        metadata getmetadata() const;
+
+        const std::string& getfilepath() const;
+        const auto getartwork() const;
     private:
-        Metadata metadata_;
-        std::string filePath_;
+        metadata metadata_;
+        std::string filepath_;
+        fs::path musicdir = music_folder;
 };