Refactor GameType enum for improved readability and clarity

[teogor]

This pull request refactors the GameType enum to improve its readability and clarity. The following changes were made:

• Renamed the sectionHeight and sectionWidth parameters to gridHeight and gridWidth, respectively, to better reflect their intended meaning.
• Added a cells property that returns the total number of cells in the puzzle, making it easier to access this information without having to calculate it manually.
• Added an isSquare property that returns whether the puzzle is a square, providing a convenient way to check this property.
• Modified the toString() method to return a string representation of the game type in the format {cells}x{cells}, making it more concise and informative.

These changes make the GameType enum more consistent, easier to understand, and more convenient to use.