Function compile_frontend_with_options 

pub fn compile_frontend_with_options(
    source: &str,
    preview_features: &PreviewFeatures,
) -> MultiErrorResult<CompileState>

Compile source code through all frontend phases.

This runs: lexing → parsing → AST to RIR → semantic analysis → CFG construction. Returns the compile state which can be inspected for debugging.

This function collects errors from multiple functions instead of stopping at the first error, allowing users to see all issues at once.