Expand description
Build-time version information, for caproni version’s output.
Ported from internal/buildinfo/buildinfo.go. Go injects version,
commit, and date via goreleaser’s -ldflags, defaulting to
"dev"/"unknown"/"unknown" in a plain go build. This port uses
env!("CARGO_PKG_VERSION") for version() (always accurate; Cargo
always knows it, unlike Go’s zero-value default), and option_env! for
commit()/date(), which a release build sets via XIANYUN_BUILD_COMMIT/
XIANYUN_BUILD_DATE environment variables at compile time, falling back
to the same "unknown" Go defaults to otherwise.