[TypeDeclaration] Drop AstResolver from NarrowObjectReturnTypeRector parent check

[TomasVotruba]

What

NarrowObjectReturnTypeRector::isNarrowingValidFromParent() resolved each ancestor's method into a full AST (AstResolver->resolveClassMethod()) only to read two things:

1. the parent's native return type (must be a single bare class name), and
2. whether the parent's @return is a generic type (e.g. Collection<int, Foo>), which blocks narrowing.

Both are available from PHPStan's ExtendedMethodReflection without re-parsing the source file:

$parametersAcceptor = ParametersAcceptorSelector::combineAcceptors(
    $ancestor->getNativeMethod($methodName)->getVariants()
);

$parentNativeReturnType = $parametersAcceptor->getNativeReturnType();   // native return
$parametersAcceptor->getReturnType();                                   // phpdoc-merged return

• getNativeReturnType() → replaces the Identifier/FullyQualified node check. We keep only ObjectType (single bare class); object-keyword, union, nullable, scalar all map to non-ObjectType and are skipped exactly as before.
• getReturnType() instanceof GenericObjectType → replaces reading the parent node's docblock via PhpDocInfoFactory. PHPStan resolves @return Collection<int, Foo> to a GenericObjectType, and @return T (template) to a non-generic type — matching the previous behaviour.

Why

AstResolver re-parses the declaring file of every ancestor on every matching method. The data needed here is pure type metadata that reflection already holds, so the parse was overhead. The earlier "docblock = AST-only" assumption only holds for raw docblock text; the semantic generic-type check is fully available via getReturnType().

Tests

All existing fixtures pass unchanged, including the parent-path cases (narrow_with_generic_parent, narrow_parent_has_specific_return_type, narrow_from_abstract_class, narrow_from_parent_to_child). vendor/bin/phpunit rules-tests/TypeDeclaration/Rector/ClassMethod/NarrowObjectReturnTypeRector → 14/14 green. ECS + PHPStan level 8 clean.