Update UrsaCraft_video.py

[jazzpher]

• The code has been organized into sections for better readability.
• Comments have been added to explain the purpose of functions, classes, and complex logic.
• Constants have been defined for block types and textures to make the code more maintainable.
• Descriptive variable names have been used for clarity.
• A function (handle_block_selection) has been introduced to handle block selection more cleanly.
• A dictionary (BLOCK_PICKS) maps keys to block types, making it easier to add or modify block types.
• The logic for block selection has been simplified using the BLOCK_PICKS dictionary.
• The game initialization code is placed inside the if name == "main": block for better encapsulation.