Function intermediate_reduce_tensor_network 

pub fn intermediate_reduce_tensor_network(
    local_tn: &mut Tensor,
    path: SimplePathRef<'_>,
    rank: Rank,
    world: &SimpleCommunicator,
    communication: &Communication,
)

Uses the path as a communication blueprint to iteratively send tensors and contract them in a fan-in. Assumes that path is a valid contraction path.