feat: generate #[Async] actions with pollora:make:action --async

[ogorzalka]

Phase 4 of Async Actions, step 3: pollora:make:action --async generates the method with #[Async] and its import, both in a new class and when the method is added to an existing class.

Two generator fixes found while testing:

• pollora:make:action and pollora:make:filter were registered under the names pollora:make:action {name} and pollora:make:filter {name}. The console reached them by prefix match, but Artisan::call('pollora:make:action') failed with "command does not exist".
• For a hook with separators, the generated method was named handleSavepost (from save_post). It is now handleSavePost.

Tests: ActionMakeCommandTest (3), the first tests for this generator. 1897 tests pass, PHPStan clean.