Function compile_page_assets 

pub fn compile_page_assets(
    entry_path: &str,
    files: &HashMap<String, String>,
    data_json: &str,
    asset_prefix: &str,
) -> Result<PageAssets, String>

Compile a multi-file .van project with separated assets.

Like compile_page, but returns HTML + assets map instead of a single HTML string. CSS/JS are returned as separate entries, HTML references them via <link>/<script src>.