WiFi and Ethernet library problems. Solutions:

The MbedClient is not copyable. There is an attempt to make it survive one copy right after creation, which should work for returning a copy from server.available() but that is not good enough.

Issues:
https://github.com/arduino/ArduinoCore-mbed/issues/753
https://github.com/arduino/ArduinoCore-mbed/issues/715

I have a simple fix for the copyability of Client. It just have to test it thoroughly yet. PR https://github.com/arduino/ArduinoCore-mbed/pull/768

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The MbedServer doesn't manage connected clients as it should for proper implementation of available and print-to-all-clients. `available()` here works like Ethernet library's `accept()` and print-to-all-clients attempts to send a buffer with the listening socket which is not supported in Mbed/LwIP.

I can fix MbedServer too, but in which way? Implement `available()` and print-to-all-clients? It would break `available()` for users which already use it as it is? Just rename `available()` to `accept()` and add `available()` as a deprecated alias to `accept()`? And then even remove inheritance from Server/Print and the write methods, or just leave them with empty implementation?

Start with the MbedClient and MbedServer entry points, especially available(), accept(), print-to-all-clients, and the Server/Print behavior. Review issues #753 and #715 plus PR #768, then determine the compatible API direction; done requires thoroughly tested client copying and resolved server-client behavior.

Written by the indexing model from the issue text.