Fix EvaluatorTest by using real CombiningMatcher instead of mock

PowerMock 1.7.4 cannot mock final classes on Java 8+. Instead of using
PowerMock, create a real CombiningMatcher instance with AllKeysMatcher,
which is a simple value object suitable for testing.

Removes PowerMock incompatibility without requiring API migration.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

AI-Session-Id: c83b3557-2c02-4d13-aaa4-273b7340163d
AI-Tool: claude-code
AI-Model: unknown

Author: gthea

client/src/test/java/io/split/engine/evaluator/EvaluatorTest.java

@@ -17,6 +17,7 @@
 
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
@@ -50,7 +51,7 @@ public void before() {
         _segmentCacheConsumer = Mockito.mock(SegmentCacheConsumer.class);
         _ruleBasedSegmentCacheConsumer = Mockito.mock(RuleBasedSegmentCacheConsumer.class);
         _evaluator = new EvaluatorImp(_splitCacheConsumer, _segmentCacheConsumer, _ruleBasedSegmentCacheConsumer, new FallbackTreatmentCalculatorImp(null));
-        _matcher = Mockito.mock(CombiningMatcher.class);
+        _matcher = CombiningMatcher.of(new io.split.rules.matchers.AllKeysMatcher());
         _evaluationContext = Mockito.mock(EvaluationContext.class);
 
         _configurations = new HashMap<>();