fix: Clean up javadoc comment formatting

- Fix line 6 javadoc comment to have correct formatting
- Remove any trailing spaces from comment line

Author: harsha08-2k6

src/main/java/com/thealgorithms/backtracking/SudokuSolver.java

@@ -3,7 +3,7 @@
 /**
  * Sudoku Solver using Backtracking algorithm
  * Solves a 9x9 Sudoku puzzle using depth-first search with backtracking
-  *
+ *
  * @author Your Name
  */
 public final class SudokuSolver {