Add ERC721 Example

[hardiktheprogrammer]

Description:

providing developers with a comprehensive set of examples, we should add an ERC721 (non-fungible token) example to the repository.

Tasks

• Create a new directory named erc721-example in the examples folder.
• Implement an ERC721 smart contract using Cairo programming language for StarkNet.
• Include necessary functions such as mint, transfer, ownerOf, balanceOf, and tokenURI.

Please assign this issue to a developer with experience in StarkNet and ERC721 token standards. Let me know if you have any further questions or requirements.