Report the module version for a go install build (closes #18)

keyfunc --version printed dev for any binary not built with make build. When no version was stamped at build time, the tool now reports the module version recorded in the binary's build info, which go install fills in. A stamped version still wins, and a local build with neither still prints dev.

Model: opus-4-8 (implementation); fable-5-1 (summary)

internal/cli/version_internal_test.go

@@ -0,0 +1,37 @@
+package cli
+
+import (
+	"runtime/debug"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestResolveVersion(t *testing.T) {
+	t.Parallel()
+
+	release := &debug.BuildInfo{Main: debug.Module{Version: "v1.2.3"}}
+	local := &debug.BuildInfo{Main: debug.Module{Version: "(devel)"}}
+	empty := &debug.BuildInfo{}
+
+	t.Run("stamped value wins over build info", func(t *testing.T) {
+		t.Parallel()
+		require.Equal(t, "v0.1.0", resolveVersion("v0.1.0", release))
+	})
+
+	t.Run("go install reports the module version", func(t *testing.T) {
+		t.Parallel()
+		require.Equal(t, "v1.2.3", resolveVersion(devVersion, release))
+	})
+
+	t.Run("a local build stays dev", func(t *testing.T) {
+		t.Parallel()
+		require.Equal(t, devVersion, resolveVersion(devVersion, local))
+	})
+
+	t.Run("no version anywhere stays dev", func(t *testing.T) {
+		t.Parallel()
+		require.Equal(t, devVersion, resolveVersion(devVersion, empty))
+		require.Equal(t, devVersion, resolveVersion(devVersion, nil))
+	})
+}