Clear feature flag context cache in teardown to fix test pollution

The FeatureFlagsContextFactory caches feature flag contexts per session,
causing tests to share the same feature flag state. This resulted in the
first test creating a context with telemetry enabled, and subsequent tests
incorrectly reusing that enabled state even when they expected disabled.

Author: samikshya-db

tests/unit/test_telemetry.py

@@ -369,7 +369,10 @@ class TestTelemetryFeatureFlag:
 
     def teardown_method(self):
         """Clean up telemetry factory state after each test to prevent test pollution."""
+        from databricks.sql.common.feature_flag import FeatureFlagsContextFactory
+
         TelemetryClientFactory._clients.clear()
+        FeatureFlagsContextFactory._context_map.clear()
 
     def _mock_ff_response(self, mock_http_request, enabled: bool):
         """Helper method to mock feature flag response for unified HTTP client."""