Improve File installation check to handle binary files and content-mismatch errors

[coderabbitai]

Description

The current implementation of is_installed_one for File items in both Slurm and Kubernetes installers uses read_text() to compare file contents, which:

1. Raises UnicodeDecodeError for binary files
2. Returns misleading error messages when a file exists but contents differ (says 'does not exist')

Proposed Enhancement

• Use read_bytes() instead of read_text() for binary-safe comparison
• Distinguish between 'file does not exist' and 'file exists but contents differ' in error messages

References

• PR Fix installation logic for File on k8s #781:
• Comment: Fix installation logic for File on k8s #781 (comment)

Affected Files

• src/cloudai/systems/kubernetes/kubernetes_installer.py
• src/cloudai/systems/slurm/slurm_installer.py

/cc @amaslenn