Add a new devel/libks port for SignalWire's libks support library.
libks provides common C utility code used by SignalWire and related projects, including platform abstraction, threading, networking, JSON, UUID, TLS, logging, buffers, and general helper routines.
The upstream repository is named libks, but the installed ABI and package metadata use the libks2 name. Upstream installs libks2.so, libks2 pkg-config metadata, CMake config files, headers under include/libks2, and documentation under share/doc/libks2.
This includes local FreeBSD compatibility patches for platform detection, UUID headers, and thread ID handling.