Function try_forward 

pub fn try_forward<Op: Primitive>(
    output_key: &ValueKey<Op>,
    output_trace: Option<&Trace<Op>>,
    tangent_seeds: &HashMap<ValueKey<Op>, Arc<Op::Operand>>,
    executor: &mut impl ForwardExecutor<Op>,
    ctx: &mut Op::ADContext,
) -> ADRuleResult<Option<Arc<Op::Operand>>>
where
    Op::InputKey: ADKey,

Execute forward-mode AD over an eager trace for one output value.