fix(file): ensure directory creation and preserve generic types

[theEvilReaper]

Proposed changes

This PR improves ModernGsonFileHandler and GsonFileHandler by ensuring missing parent directories are automatically created when saving files, preventing NoSuchFileException errors. Additionally, it fixes an issue where generic type parameters were stripped during JSON serialization due to typeToken.getRawType(), and corrects the new file logging check. Common path preparation logic has been extracted into FileHandlerUtil to eliminate code duplication, and the test suite has been refactored for full test isolation

Types of changes

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• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (if none of the other choices apply)

Checklist

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• I have read the CONTRIBUTING.md
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)