Function render_template_to_string 

pub fn render_template_to_string(
    template: &str,
    bindings: Option<&BTreeMap<String, VmValue>>,
    base: Option<&Path>,
    source_path: Option<&Path>,
) -> Result<String, String>

Render a template for callers outside the VM crate that need the same prompt-template semantics as render(...) / render_prompt(...).