internal: clean up build strings

These names are less ambiguous and should be understandable without reading the source code.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/version.go

@@ -0,0 +1,19 @@
+package internal
+
+// FallbackVersion is returned when a version string was not set by the linker.
+const FallbackVersion = "dirty"
+
+// buildVersion is the Hakurei tree's version string at build time.
+//
+// This is set by the linker.
+var buildVersion string
+
+// Version returns the Hakurei tree's version string.
+// It is either the value of the constant [FallbackVersion] or,
+// when possible, a release tag like "v1.0.0".
+func Version() string {
+	if buildVersion != "" {
+		return buildVersion
+	}
+	return FallbackVersion
+}