refactor: require pollora/attributes instead of shipping the attributes

[ogorzalka]

Second step of the pollora/attributes extraction, after #462. The attributes now come from pollora/attributes (v0.1.0), which the framework requires as ^0.1 || ^1.0. No class name changes.

What moves

• src/Attributes/* (112 files) and the value types the attributes take: Pollora\Schedule\Every, Interval, Pollora\Role\Domain\Enums\Access, Pollora\Meta\Domain\Enums\Control, Pollora\BlockBinding\Domain\Enums\BindingFieldType. The package declares these under their exact namespaces; Composer still finds the framework's other classes of those namespaces in src/.
• 9 tests that only touch attributes (HookTest, PostTypeAttributeTest, PostTypeSubAttributesTest, ScheduleTest, TaxonomySubAttributesTest, NamingTest, ArchitectureTest, EveryTest, IntervalTest), now in the package with a test of what each attribute contributes.

What stays

• The two deprecated bases, PostTypeAttribute and TaxonomyAttribute (they need the framework's interfaces), and every discovery that reads the attributes.
• #[SkipDiscovery] stays in pollora/discovery. pollora/attributes requires pollora/ajax and pollora/abilities for AjaxAccess and Behaviour; both depend on PHP alone.
• SlugTest added: Pollora\Support\Slug delegates to the package's naming helper, whose parity test moved with it.

Checks

Against the package as a path repository: 1878 tests (1975 before, 97 moved to the package, which runs 114), PHPStan 0, type coverage 99.1 %.

CI needs pollora/attributes on Packagist to install; it is re-run once the package is indexed.