Update Simple Library Server

[radeusgd]

Pull Request Description

Updates the simple library server in preparation for our deployment.

• Support for the PORT environment variable.
• Making it more robust: atomic move for committing the upload, handling signals for graceful shutdown.

Important Notes

Checklist

Please include the following checklist in your PR:

• The documentation has been updated if necessary.
• All code conforms to the Scala, Java, and Rust style guides.
• All documentation and configuration conforms to the markdown and YAML style guides.
• All code has been tested where possible.