Test: Add comprehensive holdout test scenarios aligned with Swift SDK

- Add decideAll tests with various holdout configurations (global, included, excluded, multiple)
- Add holdout status tests (Draft, Concluded, Archived should not apply)
- Add impression event metadata tests
- Add test for holdout impressions with sendFlagDecisions=false
- Add audience targeting tests for holdouts
- Add enabledFlagsOnly option test
- Fix existing tests to work with Holdout entity objects (not dicts)
- Fix impression event logic to always send holdout impressions (matching Swift SDK)

All 35 holdout tests now passing, matching Swift SDK test coverage.

Author: muzahidul-opti

optimizely/optimizely.py

@@ -1260,9 +1260,10 @@ def _create_optimizely_decision(
         feature_flag = project_config.feature_key_map.get(flag_key)
 
         # Send impression event if Decision came from a feature
-        # test and decide options doesn't include disableDecisionEvent
+        # test, holdout, or send_flag_decisions is enabled
+        # Holdouts always send impressions regardless of sendFlagDecisions setting
         if OptimizelyDecideOption.DISABLE_DECISION_EVENT not in decide_options:
-            if decision_source == DecisionSources.FEATURE_TEST or project_config.send_flag_decisions:
+            if decision_source == DecisionSources.FEATURE_TEST or decision_source == DecisionSources.HOLDOUT or project_config.send_flag_decisions:
                 self._send_impression_event(project_config,
                                             flag_decision.experiment,
                                             flag_decision.variation,