std.Io.Threaded: implement netConnect with timeout

Extracted from https://github.com/ziglang/zig/pull/25592.

```zig
    if (options.timeout != .none) @panic("TODO implement netConnectIpPosix with timeout");
```

```zig
    if (options.timeout != .none) @panic("TODO implement netConnectIpWindows with timeout");
```