posix: add os.forkpty so pty.spawn does not hang - #8782

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sequenceDiagram
  participant Python_posix_forkpty
  participant VirtualMachine
  participant rustpython_host_env_posix
  participant libc
  Python_posix_forkpty->>VirtualMachine: validate finalization and fork permission
  Python_posix_forkpty->>VirtualMachine: emit audit event and run before-fork hook
  Python_posix_forkpty->>rustpython_host_env_posix: call forkpty
  rustpython_host_env_posix->>libc: call libc::forkpty
  libc-->>rustpython_host_env_posix: return pid and master_fd
  rustpython_host_env_posix-->>Python_posix_forkpty: return pid and master_fd
  Python_posix_forkpty->>VirtualMachine: run child or parent after-fork hook

Merge Risk: 🟡 Moderate · up to a86c7

The forkpty path may create a child successfully but report failure during descriptor cleanup, potentially orphaning the child and breaking PTY callers. This remains a moderate merge risk.

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📦 Library Dependencies

The following Lib/ modules were modified. Here are their dependencies:

[ ] lib: cpython/Lib/http
[ ] test: cpython/Lib/test/test_httplib.py (TODO: 1)
[x] test: cpython/Lib/test/test_http_cookiejar.py
[x] test: cpython/Lib/test/test_http_cookies.py (TODO: 1)
[ ] test: cpython/Lib/test/test_httpservers.py

dependencies:

• http (native: binascii, collections.abc, email.message, email.parser, email.utils, errno, http.client, itertools, pwd, select, sys, time, urllib.parse, urllib.request)
  • logging (native: atexit, collections.abc, email.message, email.utils, errno, http.client, logging.handlers, multiprocessing.queues, select, sys, time, urllib.parse, win32evtlog, win32evtlogutil)
  • warnings (native: _contextvars, _thread, _warnings, builtins, sys)
  • argparse, base64, calendar, contextlib, copy, datetime, enum, html, io, mimetypes, os, posixpath, re, shutil, socket, socketserver, ssl, string, subprocess, threading, traceback, types

dependent tests: (51 tests)

• http: test_docxmlrpc test_genericalias test_hashlib test_http_cookiejar test_http_cookies test_httplib test_httpservers test_logging test_robotparser test_ssl test_ucn test_unicodedata test_urllib test_urllib2 test_urllib2_localnet test_wsgiref test_xml_dom_xmlbuilder test_xmlrpc
  • logging.handlers: test_concurrent_futures test_pkgutil
  • pydoc: test_enum test_pydoc
    • pdb: test_pdb
  • urllib.request: test_pathlib test_sax test_site test_urllib2net test_urllibnet
    • pathlib: test_ast test_dbm_sqlite3 test_ensurepip test_importlib test_json test_launcher test_os test_pathlib test_peg_generator test_pyrepl test_runpy test_tarfile test_tempfile test_tomllib test_tools test_traceback test_unparse test_venv test_winapi test_zipapp test_zipfile test_zoneinfo test_zstd

Legend:

• [+] path exists in CPython
• [x] up-to-date, [ ] outdated

Merging this PR will degrade performance by 13.15%

❌ 1 regressed benchmark
✅ 61 untouched benchmarks
⏩ 4 skipped benchmarks¹

Performance Changes

_{Comparing youknowone:skip-pty-spawn-hang (967ad70) with main (854b5af)}