Function generate_solid_file 

pub fn generate_solid_file(
    manifest: &Manifest,
    client_import_path: &str,
    types_import_path: &str,
    preserve_docs: bool,
) -> String

Generates the complete SolidJS reactive primitives file content from a manifest.

Returns an empty string when the manifest contains no procedures (the caller should skip writing the file in that case).