Stdlib: fix AOT hexdec/bindec NestedJIT insert and string ABI (#26884)

[PurHur]

Summary

• Restore IR insert block after mid-emit MathBaseConvert helper/bridge link (same orphan-BB class as Regression: AOT http_build_query link fails — undefined __compiler_http_build_query (ext/standard/http.c) #26869) and skip bridge emit under NestedJIT.
• Pass __string__* into phpc_basetozval_result (NestedJIT-safe ABI) instead of i8* + stringFromCstr.
• Replace NestedJIT-fragile while/VmMath digit parse with substr recursion so AOT hexdec('ff') / bindec('1010') match Zend (255 / 10).
• Closes Regression: AOT hexdec()/bindec() compile fails — Current basic block has no parent function (ext/standard/math.c) #26884

php-src reference

• ext/standard/math.c — PHP_FUNCTION(hexdec) / PHP_FUNCTION(bindec)
• PHP implementation: ext/standard/{hexdec,bindec,octdec,base_convert_}.php, MathBaseConvertJitHelper.php, lib/JIT/Builtin/MathBaseConvert{,Runtime}.php

Test plan

• php vendor/bin/phpunit --filter 'MathBaseConvertRuntimeShrinkTest|HexdecBindecAot26884Test' → OK (7 tests)
• Docker AOT: php bin/compile.php -o /tmp/h26884 on repro → prints 255 then 10
• Docker VM: same repro → 255 / 10
• ./script/check-generated-docs.sh (Docker) → all generated docs in sync
• Not covered: full ci-local / overflow-to-float path for hexdec('FFFFFFFFFFFFFFFF') under NestedJIT (may still print 0; follow-up if needed)

Made with Cursor

[PurHur]

Merged. Verification on this branch:

php vendor/bin/phpunit --filter 'MathBaseConvertRuntimeShrinkTest|HexdecBindecAot26884Test'
# OK (7 tests, 38 assertions)

./script/docker-exec.sh -- bash -lc 'php bin/compile.php -o /tmp/h26884 build/h26884.php && /tmp/h26884'
# 255
# 10

php bin/vm.php build/h26884.php
# 255
# 10