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

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 #781:
• Comment: https://github.com/NVIDIA/cloudai/pull/781#discussion_r2708354205

Affected Files

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

/cc @amaslenn

Start with is_installed_one in src/cloudai/systems/kubernetes/kubernetes_installer.py and src/cloudai/systems/slurm/slurm_installer.py, then review the comparison and error-reporting paths. The work is done when binary files can be checked without decoding errors and the messages distinguish missing files from content mismatches in both installers.