tests: attribute scratch-file creations to the test's own process tree - #560

tests: attribute scratch-file creations to the test's own process tree and print the creator pid

test_default_scratch_tmpfs_tmpdir failed on a shared CI VM when another runner's
job created pineforge-* names in a shared temp root. At this base the default
test already uses a private TMPDIR and checks its own mkstemp descriptors, but
the witness (a) dropped creations by the test's fork descendants, (b) ignored
exclusive opens outside the private TMPDIR and (c) printed paths without any
creator identity, so a false positive could not be diagnosed from the log.

• The witness is an anonymous shared mapping inherited by fork descendants:
  creation path and creator pid are recorded by the interposed mkstemp and
  O_CREAT|O_EXCL open, after checking the returned descriptor's own
  /proc/self/fd name. No named file or endpoint a stranger could write to.
• Failures print path and pid, or "pid=unattributable" with the reason when
  only inotify saw it (inotify supplies no creator pid). Overflow, truncation
  and incomplete publication fail instead of reading as "nothing created".
• The three co-tenant rows now fork+exec a separate shell helper before the
  watches exist (released over a pipe once armed), creating names in /tmp,
  /dev/shm and /var/tmp.
• New rows: own exclusive open in /tmp is detected with path and pid, own fork
  descendant's creations are detected and attributed, diagnostics contain
  path+pid and the unattributable reason.
• scripts/ci_verify.py / test_ci_verify.py and docs/ci.md: row-count
  accounting for the three added public rows.

No engine source or public header changes.

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