Function interp_heap_peek 

fn interp_heap_peek(
    args: &[RValue],
    named: &[(String, RValue)],
    context: &BuiltinContext<'_>,
) -> Result<RValue, RError>

Peek at the maximum value in a max-heap without removing it.

Returns NULL if the heap is empty.

@param h integer scalar: heap ID @return numeric scalar (the max value), or NULL if empty