fix(lint): remove unused Settings and ProviderRegistry imports from actor tests

The PR branch accumulated two lint F401 violations in pre-existing test
file where Settings was added to an import but never used, and
ProviderRegistry was included in a parallel provider import without being
referenced anywhere in the file. Remove both to satisfy ruff checks.

tests/actor/test_registry_builtin_yaml.py

@@ -17,13 +17,12 @@ import yaml
 
 from cleveragents.actor.registry import ActorRegistry
 from cleveragents.actor.schema import ActorConfigSchema, ActorType, is_v3_yaml
-from cleveragents.config.settings import ProviderDefaults, Settings
+from cleveragents.config.settings import ProviderDefaults
 from cleveragents.core.exceptions import NotFoundError
 from cleveragents.domain.models.core.actor import Actor
 from cleveragents.providers.registry import (
     ProviderCapabilities,
     ProviderInfo,
-    ProviderRegistry,
     ProviderType,
 )