Convert all hooks to OOP format

Here is a patch that converts all hook implementations across the domain_extras package to OOP format.

Converted Modules (4 sub-modules, 5 hooks)

domain_alias_extras — 1 hook

• hook_domain_config_ui_disallowed_routes_alter -> DomainAliasExtrasHooks::domainConfigUiDisallowedRoutesAlter()

domain_access_linkit — 1 hook

• hook_node_grants_alter -> DomainAccessLinkitHooks::nodeGrantsAlter()

domain_maintenance — 2 hooks + 2 form handlers

• hook_form_system_site_maintenance_mode_alter -> DomainMaintenanceHooks::formSystemSiteMaintenanceModeAlter()
• hook_domain_delete -> DomainMaintenanceHooks::domainDelete()
• Form validate/submit handlers converted to static methods (validateForm(), submitForm()) referenced as [self::class, 'method']

domain_sso_admin_toolbar — 1 hook

• hook_toolbar_alter -> DomainSsoAdminToolbarHooks::toolbarAlter() with injected current_user, entity_type.manager, and domain.negotiation_context services

For each module

• Created src/Hook/*Hooks.php with #[Hook] attributes
• Created or updated *.services.yml with service definitions
• Updated .module files with #[LegacyHook] delegations for Drupal 10.6 backward compatibility

Tests

All 11 existing tests pass (95 assertions) across 4 test suites: domain_access_linkit kernel test, domain_maintenance functional test, domain_sso functional test, and domain_sso_admin_toolbar functional tests (8 methods).