Remove the JNA dependency, use JDK unix domain socket support

Since CONJ-1354 replaced waffle-jna with the JDK native GSS-API bridge, JNA (net.java.dev.jna:jna and jna-platform, both optional) was used only by the socket layer:

• UnixDomainSocket bound libc socket / connect / recv / send / close through Native.register("c") to implement the localSocket option.
• NamedPipeSocket called Kernel32.WaitNamedPipe when a Windows pipe was busy, with a sleep-and-retry fallback already in place for when JNA was absent.
• SocketUtility called Platform.getOSType() only to detect JNA presence.

Java 16 provides unix domain sockets natively through SocketChannel.open(StandardProtocolFamily.UNIX) and UnixDomainSocketAddress, so no native access library is needed.