Use strict maybe types in TCPIP library

There are two versions of a non-blocking TCP interface used in ObjectIO. One is in TCPIP/ObjectIO, the other in ObjectIO/Tcp. It is not clear to me which is newer. I have adapted the one in TCPIP/ObjectIO, so that compilation succeeds, but have not tested it because I could not find an example using it. (It is also not included in any distribution.) I have not touched ObjectIO/Tcp, since it is broken (seq undefined). I will open a separate issue to see what to do with these modules.

Once this is merged, clean-platform!358, iTasks-SDK!463, and https://gitlab.science.ru.nl/cloogle/cloogle-org/-/merge_requests/226 will have to be merged as well.