Race Condition vulnerability

[th555555]

This PR fixes a race condition vulnerability in the createTempDirectory method that could allow attackers to exploit the gap between file deletion and directory creation

Problem
The original implementation used an unsafe pattern:

1. Create a temporary file with File.createTempFile()
2. Delete the file with temp.delete()
3. Create a directory with the same name using temp.mkdir()

This creates a window where an attacker could:

• Create a symbolic link pointing to sensitive directories
• Create files/directories they control
• Potentially escalate privileges or access unauthorized resources

Solution
Replace the unsafe temporary directory creation with Files.createTempDirectory() from Java NIO.2, which creates directories atomically and securely without the race condition

References:
https://cwe.mitre.org/data/definitions/362.html
UniversaBlockchain/universa@1e34b18