[Chemaclass]

Background

Closes #1402. Snapshot values such as -n were consumed as echo flags and saved as empty files. Creating and updating snapshots now writes them literally.

Changes

• Use printf for both snapshot writes, preserving the existing trailing newline.
• Verify create, repeat comparison and update for -n, -e, -E and combined flags.
• Focused checks: 60 snapshot cases, 47 strict cases, 47 on Bash 3.0 (three expected skips), ShellCheck and formatting.

Checklist

• I updated the CHANGELOG.md to reflect the new feature or fix
• I updated the documentation to reflect the changes (the documented snapshot behavior is unchanged)