php-in-php: route session_create_id JIT through VmSession PHP (#9500)

[PurHur]

Summary

• Add ext/standard/SessionCreateIdJitHelper.php delegating to VmSession::createId() (php-src ext/session/session.c)
• Shrink lib/JIT/Builtin/SessionCreateIdRuntime.php from 287 → 235 LOC: delete hex-table / __compiler_random_bytes LLVM entropy loop; keep thin ABI bridges only
• Add SessionCreateIdRuntimeShrinkTest + spine require_once for self-host

Closes #9500

C runtime shrink

No new runtime/*.c symbols. Removed ~80 lines of hand-maintained LLVM ID generation (hex encode loop, HEX_TABLE global).

Verification

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh
vendor/bin/phpunit --filter SessionCreateIdRuntimeShrinkTest
vendor/bin/phpunit --filter session_create_id test/compliance/
php bin/vm.php test/compliance/cases/stdlib/session_create_id_jit.phpt
php bin/jit.php test/compliance/cases/stdlib/session_create_id_jit.phpt
'
make bootstrap-selfhost-vm-driver-execute-probe
php script/check-selfhost-spine-coverage-sync.php

Output:

OK (3 tests, 12 assertions)          # SessionCreateIdRuntimeShrinkTest
OK (4 tests, 4 assertions)          # compliance session_create_id*
idok / prefixed                     # VM + JIT phpt
bootstrap-selfhost-vm-driver-execute-probe: OK
check-selfhost-spine-coverage-sync: OK

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