fix: remove stdout prints, improve test determinism, and update trace handling

Removed `print` statements from the `LLMStreamChunkEvent` handler to prevent
LLM response chunks from being written directly to stdout. The listener now
only tracks chunks internally.

Fixes #3715

Added explicit return statements for trace-related tests.

Updated cassette for `test_failed_evaluation` to reflect new behavior where
an empty trace dict is used instead of returning early.

Ensured deterministic cleanup order in test fixtures by making
`clear_event_bus_handlers` depend on `setup_test_environment`. This guarantees
event bus shutdown and file handle cleanup occur before temporary directory
deletion, resolving intermittent “Directory not empty” errors in CI.

lib/crewai/tests/conftest.py

@@ -160,11 +160,13 @@ def mock_opentelemetry_components():
 
 
 @pytest.fixture(autouse=True)
-def clear_event_bus_handlers():
+def clear_event_bus_handlers(setup_test_environment):
     """Clear event bus handlers after each test for isolation.
 
     Handlers registered during the test are allowed to run, then cleaned up
     after the test completes.
+
+    Depends on setup_test_environment to ensure cleanup happens in correct order.
     """
     from crewai.events.event_bus import crewai_event_bus
     from crewai.experimental.evaluation.evaluation_listener import (
@@ -173,6 +175,7 @@ def clear_event_bus_handlers():
 
     yield
 
+    # Shutdown event bus and wait for all handlers to complete
     crewai_event_bus.shutdown(wait=True)
     crewai_event_bus._initialize()