chore: prune mypy exclude list (#3561)

# What does this PR do?

prune the mypy exclude list, build a stronger foundation for quality
code


## Test Plan

ci

llama_stack/providers/utils/inference/model_registry.py

@@ -20,7 +20,7 @@ logger = get_logger(name=__name__, category="providers::utils")
 
 
 class RemoteInferenceProviderConfig(BaseModel):
-    allowed_models: list[str] | None = Field(
+    allowed_models: list[str] | None = Field(  # TODO: make this non-optional and give a list() default
         default=None,
         description="List of models that should be registered with the model registry. If None, all models are allowed.",
     )