Using C++20 coroutines to handle messages in agents

Hello! Have you considered using coroutines to process messages in agents? It would be good solution for waiting messages with saving context.

Something like that
```cpp
class SomeAgent: public agent_t
{
// ...

coro_type sendRequestWaitResponse()
{
    so_5::send<Request>(someMbox);
    auto response = co_await so_5::receive<Response>(someMbox);
    // handle response
}

//...
};
```