fix(fs): differential-test and reclassify basis dirs, delay-updates, fuzzy, dry-run

Each row's exact residual reproduced against rsync 3.4.1:
- basis dirs (--compare/copy/link-dest): FastSync xxHash-verifies a basis hit
  while rsync --size-only installs the wrong same-size basis content.
- --delay-updates: the fixed .fastsync-stage name wipes an unrelated
  destination entry of that name even without --delete; rsync leaves it.
- --fuzzy: deterministic name/size heuristic (10x window), not rsync's matcher.
- --dry-run: would-delete report over-reports the updated file and an
  excluded-but-protected extra, and ordering differs.
Docs: RSYNC_COMPAT tally 109/16/31; HANDOFF item 9. clang-format + cppcheck +
ASan + full suite clean.

src/shared/file.c

@@ -816,8 +816,8 @@ bool file_ensure_directory_secure(const char* path) {
        replacing it is not required for FastSync's transferred directories and
        keeps --keep-dirlinks semantics untouched. */
     struct stat leaf_st;
-    if (fstatat(parent_fd, leaf, &leaf_st, AT_SYMLINK_NOFOLLOW) == 0 &&
-        !S_ISDIR(leaf_st.st_mode) && !S_ISLNK(leaf_st.st_mode)) {
+    if (fstatat(parent_fd, leaf, &leaf_st, AT_SYMLINK_NOFOLLOW) == 0 && !S_ISDIR(leaf_st.st_mode) &&
+        !S_ISLNK(leaf_st.st_mode)) {
       if (unlinkat(parent_fd, leaf, 0) == 0) {
         if (mkdirat(parent_fd, leaf, (mode_t)(0777 & ~(mode_t)file_process_umask())) == 0) {
           created = true;