Fix duration saying never when it's unlimited

internal/config/parse.go

@@ -103,6 +103,16 @@ func ParseDuration(s string) (time.Duration, error) {
 	return d, nil
 }
 
+// FormatLifetime renders a lifetime *limit*, where FormatDuration's "never"
+// would describe the wrong thing: a ceiling of Unlimited is not a file that
+// never expires, it is the absence of a ceiling.
+func FormatLifetime(d time.Duration) string {
+	if d == Unlimited {
+		return "unlimited"
+	}
+	return FormatDuration(d)
+}
+
 // FormatDuration is the human-facing inverse of ParseDuration.
 func FormatDuration(d time.Duration) string {
 	switch {