Improve EOF error messages on schema validation

[ehennestad]

What changed

Improved the end-of-file validation messages in openMINDS_validation/utils.py by:

• short file check so files under 2 bytes fail with a more accurate message
• added a clearer message for files that do not end with a closing } followed by a single newline

Why

The previous EOF check could report misleading errors for some invalid file endings. For example, when validating a file with 2 newline characters at the end of the file, the error would state: No newline at end of file

Impact

Schema validation failures caused by invalid file endings should now be easier to understand and fix.

Validation

• parsed openMINDS_validation/utils.py successfully with ast.parse
• did not run the full validator flow