build.rs captures the short git SHA at compile time via
`git rev-parse --short HEAD` and emits it as GIT_SHORT_SHA. Falls back
to "unknown" when git is unavailable (e.g. Nix sandboxed builds).
main.rs adds a VERSION const (`env!("CARGO_PKG_VERSION") + "+" + SHA`)
and passes it to clap's `version =` attribute, enabling both -V and
--version flags.
Example output: `nbd 0.1.0+8f4d25b`
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Elijah Voigt