Remove deprecated serial_sequential.h header and update includes in cpp_core.h

- Deleted the `serial_sequential.h` header to streamline the codebase and eliminate unused functionality.
- Updated `cpp_core.h` to include the new `sequential.h` header, enhancing organization and maintainability of the serial interface.

These changes align with ongoing refactoring efforts to improve header management and code clarity.

Author: Katze719

include/cpp_core.h

@@ -13,7 +13,7 @@
  */
 
 #include "cpp_core/error_callback.h"
+#include "cpp_core/interface/sequential.h"
 #include "cpp_core/serial.h"
-#include "cpp_core/serial_sequential.h"
 #include "cpp_core/status_codes.h"
 #include "cpp_core/version.h"