php-in-php: VmFsTouch/VmFsTempnam — pure PHP, drop libc FFI (#12145)

[PurHur]

Summary

• Add VmFsTouchPure (create via VmFsOpenNative, times via bootstrap touch())
• Add VmFsTempnamPure (exclusive-create loop with mode x)
• VmFsTouchNative / VmFsTempnamNative delegate to Pure — ~180 lines of libc FFI removed
• VmTmpfilePure falls back to php://temp when mkstempOpen unavailable
• Spine: VmFsTouchPure.php, VmFsTempnamPure.php

Closes #12145

php-src reference

• ext/standard/filestat.c — php_touch
• ext/standard/file.c — tempnam

C/runtime shrink

• Deleted utime/stat/open FFI table from VmFsTouchNative.php
• Deleted mkstemp/close/unlink FFI table from VmFsTempnamNative.php

Verification

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh
php script/check-selfhost-spine-coverage-sync.php
vendor/bin/phpunit --filter "VmFsTouchTempnam|VmFsRuntimeShrink|FsDirRuntimeShrink|VmTmpfilePure"
'
make bootstrap-selfhost-vm-driver-execute-probe

check-selfhost-spine-coverage-sync: OK (3279 files)
PHPUnit — OK (20 tests, 104 assertions)
bootstrap-selfhost-vm-driver-execute-probe: OK

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