Add TypeScript types for parsers

**Problem**
When working with lib, the error messages could be more descriptive.

**Suggestion**
Improve error handling and add detailed error messages.

**Context**
This would help with debugging and maintenance.

The issue names parsers but provides no file, test, or entry point. Start by locating the parser implementation and its error paths; done should mean parser types are added and error messages are more descriptive, with focused checks for the resulting behavior.

Written by the indexing model from the issue text.