Implemented the From trait for converting mio socket types into std

[tglane]

Implemented the following traits for conversion between the mio socket types and the std socket types:
From<mio::net::UdpSocket> for std::net::UdpSocket;
From<mio::net::TcpListener> for std::net::TcpListener;
From<mio::net::TcpStream> for std::net::TcpStream;

This allows the conversion without using the unsafe keyword in the user code. Inside of the trait function we use the unsafe keyword to access the raw underlying socket of the mic sockets. But since the mid socket types are in a well-defined state after construction, the use of unsafe here should be safe.

Closes #1754

[Thomasdezeeuw]

Two small suggestions, if you can apply those to all implementations this LGTM.

Could you also add From implementations for the Unix-only UDS types in src/net/uds?

[tglane]

Two small suggestions, if you can apply those to all implementations this LGTM.

Could you also add From implementations for the Unix-only UDS types in src/net/uds?

I added the trait implementation for UnixDatagram, UnixStream and UnixListener as well.

[Thomasdezeeuw]

This currently fails to build on WASI. Can you try the following, to see if that fixes it? You might need to add use std::os::wasi::io::{FromRawFd, IntoRawFd}; to some files.

Suggested change

	#[cfg(any(unix, target_os = "hermit"))]
	#[cfg(any(unix, target_os = "hermit", target_os = "wasi"))]

[tglane]

Sure. With that addition the lib can be built for the target wasm32-wasi on my machine.

Edit: We still get failing CI tasks but they do not seem to be related to the changes made in this PR since the same tasks fail in other MR as well.

[Thomasdezeeuw]

Thanks @tglane