Fix BackedEnum from()/spaceship var_dump dead call-arg slot (#9575)

[PurHur]

Summary

• Extend the Language: backed enum class const fetch (E::Case) must yield enum case objects not backing scalars (Zend/zend_enum.c) #9030 dead call-arg temp wiring in findInlineExprCallArgProducerSlot() to TYPE_LONG (spaceship <=> results), so var_dump(E::A <=> E::from(1)) passes the comparison int instead of a stale enum-case slot.
• Add maintainer repro test/repro/maintainer_enum_from_regression.php and a compile-time guard in InlineCallArgProducerSlotTest.

Root cause: BackedEnum::from() / tryFrom() lookup was already correct on VM/JIT; the reported regression surfaced via enum_from_spaceship.phpt where php-cfg emits a dead arg temp for var_dump() and the compiler only rewired boolean producers (#9030), not int-producing spaceship ops nested with E::from().

php-src reference: Zend/zend_enum.c — zend_enum_from_case(); compile-time call-arg lowering mirrors zend_compile.c dead-temp behavior (#9030).

Test plan

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh
php test/repro/maintainer_enum_from_regression.php
php bin/vm.php test/repro/maintainer_enum_from_regression.php
php bin/jit.php test/repro/maintainer_enum_from_regression.php
vendor/bin/phpunit --filter enum_from
vendor/bin/phpunit test/unit/InlineCallArgProducerSlotTest.php --filter testVarDumpSpaceshipFromSendsSpaceshipResultSlot'

Verified output (2026-06-18)

# maintainer repro (VM)
enum(Color::Red)
enum(Color::Red)
enum(Count::One)
enum(Count::One)
from_invalid: "nope" is not a valid backing value for enum Color
NULL

# enum_from_spaceship.phpt (VM)
int(0)
int(0)
int(0)

# enum_from filter: 11/12 pass (VM + JIT spaceship green); pre-existing AOT try/catch ValueError gap on fixtures/aot/cases/enum_from.phpt unchanged

Closes #9575

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