Add optional POSIX-compliant directory nlink counting
(nlink = 2 + number_of_subdirectories) behind the -posixDirNlink
flag. This requires listing cached directory entries on every stat,
which has a performance cost, so it's off by default.
When disabled (default), directories report nlink=2, which is the
POSIX-compliant baseline for empty directories and a common default
in distributed filesystems.
- Set nlink baseline to 2 for all directories (was 1)
- Add applyDirNlink() gated behind option.PosixDirNlink
- Add -posixDirNlink CLI flag
178532e63a