Reject #[\Override] on trait-provided methods at compile time (#6440)

[PurHur]

Summary

• #[\Override] no longer treats trait-composed methods as valid override targets — matches php-src zend_compile.c (parent class + interface chain only).
• Removed trait lookup from ClassCompileRegistry::hasOverridableMethod() / findOverriddenMethod() and simplified OverrideValidator.
• Updated compliance + unit tests; direct trait override and trait-alias child override both fail at compile time.

Closes #6440

php-src reference

• Zend/zend_compile.c — ZEND_ACC_OVERRIDE validation walks parent class chain only; trait methods are not override targets (PHP 8.3+)

Verification

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && vendor/bin/phpunit --filter OverrideAttributeTest'
# OK (4 tests, 7 assertions)

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && vendor/bin/phpunit --filter "override_trait|override_trait_method|override_trait_alias"'
# OK (6 tests, 6 assertions) — VM + JIT compliance

Issue repro (compile-time fatal, exit 255):

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh
cat > /tmp/override_trait_direct.php <<'"'"'PHPEOF'"'"'
<?php
trait T { public function f(): void {} }
class C { use T; #[\Override] public function f(): void {} }
PHPEOF
php bin/vm.php /tmp/override_trait_direct.php; echo exit:$?'
# CompileError: C::f() has #[\Override] attribute, but no matching parent method exists
# exit:255

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