Shared Library Support

As currently implemented, there is a clean `ds4.h` and `ds4.c` which create a static library that is consumed by the C programs `ds4-server` and `ds4-agent` and various other tools.

Despite the clean interface, the project does not currently provide a shared library and the current implementation includes `stderr` output and `exit`. Containing and routing the logs and exits would allow other callers to use the library.

With that, the `ds4` API and shared library could be wrapped for use in other languages. Then it can be a high performance inference engine with focused Metal/CUDA kernels and CPU scaffolding.

Then developers can make `ds4` applications in other languages.

I've been working on it at this branch, which also has CI/CD for generating signed binaries:
* https://github.com/NimbleMarkets/ds4/tree/nm-shared

Using that, I made a Golang wrapper, including an opinionated TUI installer of those signed binaries and resumable model downloader, and Golang ports of the sample programs:
* https://github.com/NimbleMarkets/ds4go

I used it end-to-end with Charm Crush (after making a Fantasy provider) with some other work and am playing with BubbleTea demos which I'll share when they are tighter. Playing with this has surfaced issues all over the place!