Add AttributeGenerator and class-level attribute support

[armenio]

Q	A
Documentation	no
Bugfix	no
BC Break	no
New Feature	yes
RFC	no
QA	no

Description

Laminas\Code\Generator currently has no way to emit PHP attributes, so any class generated
through this library loses them. This is a long-standing gap: attributes have been part of the
language since PHP 8.0, and consumers such as proxy generators and ORM/DI tooling need to emit
them. See #144, and the earlier attempt in #145.

This PR adds Laminas\Code\Generator\AttributeGenerator plus attribute support on
ClassGenerator (and, by inheritance, InterfaceGenerator and TraitGenerator). It targets
4.18.x as a new feature, and is fully backwards compatible: no existing behaviour changes, and
no existing output changes.

How the code is used

$class = new ClassGenerator('MyEntity');
$class->setAttributes([
    AttributeGenerator::fromName(Entity::class),
    AttributeGenerator::fromName(Table::class, ['name' => 'my_entity']),
]);
$class->addAttribute(AttributeGenerator::fromName('My\Attributes\Deprecated', ['since 1.2.0']));

echo $class->generate();

#[\Doctrine\ORM\Mapping\Entity]
#[\Doctrine\ORM\Mapping\Table(name: 'my_entity')]
#[\My\Attributes\Deprecated('since 1.2.0')]
class MyEntity
{
}

Attributes on existing symbols can be read back through reflection:

// list<AttributeGenerator>
$attributes = AttributeGenerator::fromReflector(new ReflectionClass(MyEntity::class));

Public API

• AttributeGenerator::fromName(string $name, array $arguments = []): self
• AttributeGenerator::fromReflectionAttribute(ReflectionAttribute $attribute): self
• AttributeGenerator::fromReflector(ReflectionClass|ReflectionClassConstant|ReflectionFunction|ReflectionMethod|ReflectionParameter|ReflectionProperty $reflector): list<self>
• AttributeGenerator#generate(): string, #getName(), #getArguments()
• ClassGenerator#setAttributes(list<AttributeGenerator>), #addAttribute(), #getAttributes()

Everything else is private. The class is final, @psalm-immutable, implements
GeneratorInterface only, and is not Stringable.

Design notes

This is a fresh implementation rather than a rebase of #145, written against the design direction
requested there by @Ocramius: a single class with a thin public API and no separate
assembler/builder/factory layer.

• No ::fromArray(), per Deprecating all ::fromArray() methods in in the package #153.
• No AttributeBuilder / AttributeAssembler / AttributeAssemblerFactory / AttributePart.
  Since the assembler layer is gone, the open "should AttributePart become an enum" question from
  Support for PHP 8.0 class attributes generation #145 no longer applies: there is no part type left to model.
• Names are always emitted fully qualified (#[\Foo\Bar]), so output is valid regardless of the
  surrounding use statements. A leading \ in the input is accepted and normalised away.
• Argument values are rendered by a private renderer rather than ValueGenerator. Attribute
  arguments are constant expressions with different rules than property defaults, and
  ValueGenerator renders 1.0 as 1, silently changing the argument's type. Supported values:
  null, bool, int, float, string, array (recursive, list and hash) and enum cases.
  Anything else throws InvalidArgumentException.
• Invalid input fails at construction time where practical: malformed attribute names,
  malformed argument names, and positional arguments following named ones are all rejected by
  fromName().
• ClassGenerator::fromReflection() deliberately does not populate attributes. Doing so would
  silently change the output for every existing consumer that generates classes from reflection —
  proxy generators in particular. Attributes are opt-in via AttributeGenerator::fromReflector().

Scope

Class-level attributes only, matching the issue. Attributes on methods, properties, constants and
parameters are a natural follow-up and reuse AttributeGenerator unchanged — happy to add them in
a separate PR once the shape of this one is agreed.

Documentation is included in docs/book/generator/examples.md. composer cs-check,
composer test and composer static-analysis all pass locally.

Fixes #144