Improve error handling when server response can't be accommodated in the response object

[mzimbres]

For example

request req;
req.push("ping", "abc");
req.push("ping", "def");

response<std::string> res;

co_await conn.async_exec(req, res);

Allowing internal adapter code is wrong, the library should communicate an error with which the async operation will complete.

Note: This touches only responses with an static size i.e. response<T1, T2, ...> and not the generic_response.