perf(securefs): reuse name buffer and stat struct across dir entries (P2)

ober

66c056328b12eba2e62ccac81ae8c924a205e5e8

diff --git a/src/imagesite/securefs.ss b/src/imagesite/securefs.ss
index aea258b..887cda3 100644
--- a/src/imagesite/securefs.ss
+++ b/src/imagesite/securefs.ss
@@ -173,9 +173,11 @@
           (dynamic-wind
             (lambda () (void))
             (lambda ()
-              (let loop ()
-                (let ((name-bytes (make-bytevector 256 0))
-                      (info (make-info)))
+              ;; Reuse one name buffer and stat struct across every entry in
+              ;; this directory instead of allocating them per entry.
+              (let ((name-bytes (make-bytevector 256 0))
+                    (info (make-info)))
+                (let loop ()
                   (let ((name-length (c-dir-next iterator name-bytes 256 info)))
                     (cond
                       ((= name-length 0) (void))