Modernizing rs_loader: Migrating to Latest rustc Internals with HIR-based Extraction

This project aims to modernize MetaCall's rs_loader by migrating it to the latest rustc compiler internals. The current implementation relies on outdated APIs, making it incompatible with newer Rust versions. The project will focus on updating compiler integration, replacing AST-based traversal with HIR-based extraction, and adapting to changes in rustc_driver and related components. The approach includes analyzing breaking changes, incrementally migrating core modules (lib.rs, middle.rs, ast.rs), and ensuring compatibility with modern Rust toolchains. Deliverables include a fully working rs_loader compatible with the latest rustc version, improved type and function extraction using HIR, and updated documentation for maintainability.