Enhance SaveGame: java.nio.file, Try-with-Resources & Improved Error Handling

[capdevon]

This PR focuses on enhancing the stability and maintainability of the SaveGame class. By migrating to java.nio.file (NIO.2) and utilizing try-with-resources, we gain:

• Reduced resource leaks: Streams are now automatically closed.
• Adoption of java.nio.file: Replaced java.io.File with Path and Files for more reliable and cross-platform file system interactions.
• Cleaner, more readable code: Less boilerplate for stream management.
• Better diagnostics: Enhanced logging and exception handling provide clearer insights into potential issues.

Edit:
Tested with
https://github.com/jMonkeyEngine/jmonkeyengine/blob/master/jme3-examples/src/main/java/jme3test/tools/TestSaveGame.java