Fix tcp_server::bind() to not throw despite returning error_code

tcp_server::bind() was documented to return std::error_code but
internally called the throwing tcp_acceptor::listen() overload,
violating its API contract.

Add non-throwing listen() overloads to tcp_acceptor that take
std::error_code& as the last parameter, following Boost.Asio
conventions. The throwing overload now delegates to the non-throwing
implementation.

Changes:
- Add tcp_acceptor::listen(endpoint, std::error_code&)
- Add tcp_acceptor::listen(endpoint, int backlog, std::error_code&)
- Update tcp_server::bind() to use the non-throwing overload
- Add tests for success and failure paths using TEST-NET-1 addresses
- Add test for listen() on already-open acceptor behavior

Author: MungoG

doc/modules/ROOT/pages/guide/endpoints.adoc

@@ -202,7 +202,8 @@ auto [ec] = co_await s.connect(target);
 [source,cpp]
 ----
 corosio::tcp_acceptor acc(ioc);
-acc.listen(corosio::endpoint(8080));  // Bind to all interfaces
+if (auto ec = acc.listen(corosio::endpoint(8080)))  // Bind to all interfaces
+    return ec;
 ----
 
 == From Resolver Results