Low-level NIF bindings to the zvec C API.
At compile time, if the host target triple is in the supported set,
the precompiled NIF tarball for zvex-v<version> is downloaded from
GitHub releases and verified via SHA-256. If the download fails (or
the target is unsupported), zvex falls back to a source build through
Zigler + CMake (requires the Zig toolchain, CMake, and a C/C++
compiler). Set ZVEX_BUILD=1 to skip the download and force a source
build.
Prefer using the higher-level Zvex module API over calling these
functions directly.