Fix inline (int) enum cast call-arg slot wiring (#9479)

[PurHur]

Summary

• Treat Op\Expr\Cast as an inline call-arg producer so var_dump((int) E::A) wires the TYPE_CAST_INT result slot instead of the raw enum case.
• Filter dead enum ClassConstFetch preludes that feed a cast via cfgExprUsesOperand.
• Add maintainer repro, compliance guard (enum_int_cast_warning.phpt), and compile-time slot unit test.

Closes #9479

php-src reference

• Zend/zend_operators.c — cast_object / int cast on enum cases (E_WARNING + backing int)
• Zend/zend_enum.c — enum object cast rules

Verification

./script/docker-exec.sh php bin/vm.php test/repro/maintainer_gap_enum_int_cast_warning.php
# 1
# 'Object of class E could not be converted to int'

./script/docker-exec.sh php vendor/bin/phpunit --filter 'enum_int_cast_warning|InlineCallArgProducerSlotTest::testVarDumpIntCastEnumCaseUsesCastProducerSlot'
# OK (2 tests, 3 assertions)

Also verified related guard still green:

./script/docker-exec.sh php vendor/bin/phpunit --filter 'int_cast_backed_enum'
# OK (1 test, 1 assertion)

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