Minimal parser

[sidrasali]

This PR implements a basic parser for the compiler, integrating it with the existing lexer component. The implementation focuses on handling simple C-like function definitions and return statements.

Changes

• Added data classes for AST nodes
• Implemented pretty-printing functionality for AST nodes
• Added parser implementation for simple AST definition
• Added unit tests for the parser
• Created integration tests between lexer and parser

Related Issue

Closes #4