Implement a simple high-performance lexer

[Matographo]

Summary

Tokenize template input with low overhead and support the selected delimiter configuration.

Why

The lexer is the first hot path in the engine and must remain simple and fast.

Acceptance Criteria

• Representative templates tokenize correctly
• Delimiter configuration is supported where required
• Lexer behavior is covered by focused tests

Dependencies

• Depends on Specify the template language grammar #1
• Depends on Create the base project structure for CLI, engine, parser, evaluator, and config #3