Function run_r_unwind_protect 

fn run_r_unwind_protect<F, R>(f: F) -> Result<R, Box<dyn Any + Send>>
where
    F: FnOnce() -> R,

Core R_UnwindProtect wrapper. Returns Ok(result) on success, Err(payload) on Rust panic, or diverges via R_ContinueUnwind on R longjmp.

Handles: CallData boxing, trampoline, cleanup handler, continuation token, Box::from_raw reclamation on all non-diverging paths.