chore: modernize LLM interface typing and add constants (#3483)

* chore: update LLM interfaces to Python 3.10+ typing

* fix: add missing stop attribute to mock LLM and improve test infrastructure

* fix: correct type ignore comment for aisuite import

.pre-commit-config.yaml

@@ -16,3 +16,4 @@ repos:
         entry: uv run mypy
         language: system
         types: [python]
+        exclude: ^tests/