Improve Syntax Error Reporting: Add Detailed Messages and Line Numbers

[hsborges]

Currently, when a syntax error occurs in BibTeX entries, the error messages are not as informative as they could be.

Suggested enhancements:

• Display the exact line number where the syntax error has occurred.
• Provide a clearer and more descriptive error message specifying the nature of the syntax issue.
• Consider showing a snippet of the problematic entry to aid in debugging.

Benefits:

• Makes it easier for users to identify and fix BibTeX formatting errors.
• Improves the developer experience for contributors and maintainers.

Example:
Instead of showing a generic "Syntax error detected," show something like:

Syntax error: Missing comma in entry at line 23:
  @article{example,
    author = "John Doe"
    title = "Sample Paper"
    journal = "Journal Name"
  }

This improvement would help users quickly locate and resolve errors in their BibTeX files.