vibeutils 0.9.1

Patch release. Fixes correctness bugs and test infrastructure
problems exposed by tightening CI coverage after 0.9.0.

Bug Fixes

• realpath / readlink: default mode now matches GNU -E
  semantics (parent directory must be resolvable, last component
  may be missing). 0.9.0 accidentally routed default mode through
  canonicalizeMissing, allowing paths like /nonexistent/dir/file
  to succeed even when the parent was missing. New
  canonicalizeParentMustExist verifies the parent exists and
  is an actual directory (rejecting file/foo with NotDir).
• mkdir -m symbolic mode: fixed parser start base. mkdir -m go-w foo previously produced mode 0o000 (making the directory
  inaccessible even to its owner) because the local parser started
  from 0. GNU mkdir starts from 0o777. Now delegates to the
  shared common.mode.parseSymbolic with the correct base.
• mktemp: four GNU-compat fixes.
  • No-argument default template now lands in $TMPDIR//tmp
    (was: cwd).
  • User-supplied bare templates (mktemp myapp.XXX) print
    myapp.XXX verbatim, matching GNU (was: ./myapp.XXX).
  • -t with a template containing a slash now fails with
    invalid template, '...', contains directory separator.
  • ./myapp.XXX, foo/bar.XXX, and /abs/x.XXX are all
    preserved verbatim in output.
• id -G <user>: no longer hangs on macOS CI. The
  getgrouplist(3) retry loop was unbounded and held a pointer
  into libc's static getpwuid buffer across calls. Now copies
  the username into an owned buffer, caps retries at 8, and
  forces strict ngroups growth on each retry.
• tee: error messages now include the failing filename,
  matching GNU's tee: <file>: <error> format (was:
  tee: failed to open files: <error> with no file identification).

Test Infrastructure

• Add run_with_limit SECONDS CMD... helper in tests/lib/common.sh
  using Python 3 os.fork/os.execvp. Replaces GNU timeout(1),
  which macOS GitHub Actions runners lack. Used by free, sleep, tee,
  and timeout test suites.
• Add run_with_stderr_tty CMD... helper using Python 3 pty.fork
  to exercise code paths gated on isatty(stderr) (cp's overwrite
  hint). Portable across Linux and macOS.
• dd conv=swab/block/unblock/ibm/ebcdic tests now assert against
  hardcoded GNU reference bytes instead of invoking /usr/bin/dd,
  which on macOS (BSD dd) does not implement these conv modes.
• du -L/-b/-S tests assert against hardcoded byte counts instead
  of /usr/bin/du -b, which BSD du does not support.
• mkdir integration tests now numerically verify the resulting
  mode for go-w, a+rx, and u=rx — catches future regressions
  in symbolic mode parsing that the old exit-code-only assertions
  missed.
• test-privileged recipe now retries up to 3 times to absorb
  ETXTBSY flakes (Linux kernel race between linker close and
  test exec under fakeroot).

Platform Divergences Handled

• id -G <user> vs id -G count: macOS caps getgroups(2) at
  NGROUPS_MAX=16 but getgrouplist(3) is uncapped, so the named
  form can legitimately have more groups than the no-user form on
  macOS runners. Unit and integration tests relaxed to assert
  that the named form is a superset of the no-user form rather
  than strict equality.

Verified

• Full integration suite passes on both Linux (orb VM) and
  macOS CI: 48/48 utilities.
• All unit tests pass on both platforms.
• All symbolic mkdir modes (go-w, u=rwx, a+rx, u=rx,
  g=rx, u=rwx,g=rx,o=r, a+X) produce the same byte output
  as GNU coreutils 9.5 on Linux.
• All 6 dd conv modes produce GNU-matching output.