Fix convert_uu* AOT compile (bridge BB emission) — #4567

[PurHur]

Summary

• Fix AOT compile failure for convert_uuencode() / convert_uudecode() (Current basic block has no parent function on master).
• Fix AOT runtime for standalone user-script binaries: nested ConvertUuJitHelper returned corrupt encode results / segfaulted; defer to restored LLVM bodies on UserScriptAotDeferNestedJit (same pattern as base64 Stdlib/AOT: standalone binary run segfault (exit 139) after compile — Docker harness JIT-linked builtins #16734).
• JIT/embed paths unchanged — still use ConvertUuJitHelper PHP bridge (php-in-php: delete StringConvertUuJit — route convert_uuencode/uudecode through ConvertUuJitHelper PHP (#6307 follow-up) #13227).

php-src reference: ext/standard/uuencode.c — PHP bridge in ext/standard/ConvertUuJitHelper.php, standalone AOT LLVM in ext/standard/JitConvertUuBodies.php.

Closes #4567

Verification

source script/php-env.sh

# AOT compile + runtime round-trip
php bin/compile.php -o /tmp/uu - <<'PHP'
<?php
$raw = "Hello\n";
$enc = convert_uuencode($raw);
echo convert_uudecode($enc);
echo (convert_uudecode("bad") === false) ? "\nfalse" : "\nnot-false";
PHP
/tmp/uu
# Hello\n\nfalse, exit 0

vendor/bin/phpunit --filter 'AotTest::testCases.*convert_uuencode' test/aot/AotTest.php
# OK

# VM/JIT TypeError parity
php bin/vm.php test/repro-maintainer/parity_convert_uu_type.php
php bin/jit.php test/repro-maintainer/parity_convert_uu_type.php
# exit 0

vendor/bin/phpunit --filter ConvertUuRuntimeShrinkTest test/unit/ConvertUuRuntimeShrinkTest.php
# OK

./script/ci-fast.sh
# exit 0

[PurHur]

Maintainer review 2026-07-14: hold merge — PR correctly targets AOT compile (#4567 bridge BB emission) and documents the remaining AOT runtime failure (convert_uuencode return materialization). Please land runtime fix or split compile/runtime PRs; re-run vendor/bin/phpunit --filter 'AotTest::testCases.*convert_uuencode' before merge request.