add timer so that how much time has passed on a puzzle can be calculated

create 3 files named easy, medium, hard each containing at least 5 sudoku puzzles of same difficulty

implement file handling to read a random sudoku from file and display it in the sudoku_panel (already implemented)

when submit button is pressed, the sudoku is validated, if valid the time is added to high_scores file via file handling.n

multiple threads should be created (one for each row, column and 3x3 box)

each thread checks its respective row, column or 3x3 box and returns either true or false

all threads are compared and if any thread has returned false then the sudoku is invalid