fix main.go

[MonkeyKing44]

• Corrected the typo from "pupose" to "purpose" in main.go.

[vfusco]

Thank you for taking the time to contribute to our project. We truly appreciate your effort in trying to improve our documentation/code. However, per our guidelines, pull requests for simple typos or stylistic changes are not accepted. If you have ideas for broader improvements or new features, please open an issue for discussion or reach out on Cartesi Discord server. Your input is valuable, and we hope to see future contributions!