Issue #3604356: Fix remaining Drupal 12 compatibility issues on top of bot patch

Builds on the project-update-bot-only branch (!8). Adds #[RunTestsInSeparateProcesses] to kernel tests, fixes the hook_module_implements_alter regression in sites_pathauto with proper attribute-based hook ordering, converts remaining \Drupal::service() calls to DI, bumps core_version_requirement to ^11.2 || ^12, and removes the now-dead #[LegacyHook] procedural wrappers.