non-throwing overloads for `stream_file` methods

[ashtum]

The following stream_file methods currently report failures exclusively by throwing std::system_error. It would be useful to provide non-throwing overloads that accept a trailing std::error_code& parameter, aligning with existing corosio APIs (e.g. local_endpoint) and following established Asio conventions.

file_stream::open(path, mode)
file_stream::size()
file_stream::resize(new_size)
file_stream::sync_data()
file_stream::sync_all()
file_stream::assign(handle)
file_stream::seek(offset, origin)

[sgerbino]

For any API that needs to return an error in an unexceptional way, we should implement io_result return type rather than implement outparams.