Core parser and data model for HEDL format.

This crate provides the main parsing functionality for HEDL documents, including header directives, body parsing, and reference resolution.

Lexical Analysis

The [lex] module provides the complete lexical analysis infrastructure, consolidating functionality from hedl-lex, hedl-row, and hedl-tensor:

• Token validation (key tokens, type names, ID tokens, references)
• CSV/matrix row parsing with expression and tensor support
• Multi-dimensional tensor literal parsing
• Incremental parsing for IDE integration
• Source position and span tracking for error reporting

See [lex] module documentation for more details and examples.