Supports multiple senders

[sdzx-1]

There are four possibilities:

1. One sender, one receiver
2. One sender, multiple receivers
3. Multiple senders, one receiver
4. Multiple senders, multiple receivers

We have already supported 1 and 2. In both cases, the branching state is reasonable. Therefore, we choose the union as the base.

The next plan is to support 3 and 4. When there are multiple senders, branching states are definitely not possible. Therefore, choosing a struct as the base may be a better choice.