Low-level NIF bindings to the zvec C API.
At compile time mix.exs does an HTTP HEAD probe of the matching
zvex-v<version> GitHub release tarball for the host target triple. If
the release artifact is reachable and the triple is in the supported
set, the precompiled NIF is downloaded and verified via SHA-256.
Otherwise 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 probe and force a source build.
Prefer using the higher-level Zvex module API over calling these
functions directly.