Add TypeScript types for models

**Problem**
When working with parsers, 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 models, parsers, and error handling but no files or tests. Start by locating the model and parser entry points and reading the existing error handling; done means the models have TypeScript types and parser failures provide more descriptive messages.

Written by the indexing model from the issue text.