Refactor code structure for improved readability and maintainability; optimize performance in key functions.

src/Policy/StellaOps.Policy.Engine/Services/PolicyEvaluationService.cs

@@ -8,19 +8,20 @@ namespace StellaOps.Policy.Engine.Services;
 
 internal sealed partial class PolicyEvaluationService
 {
-    private readonly PolicyEvaluator evaluator = new();
+    private readonly PolicyEvaluator _evaluator;
     private readonly PathScopeMetrics _pathMetrics;
     private readonly ILogger<PolicyEvaluationService> _logger;
 
     public PolicyEvaluationService()
-        : this(new PathScopeMetrics(), NullLogger<PolicyEvaluationService>.Instance)
+        : this(new PathScopeMetrics(), NullLogger<PolicyEvaluationService>.Instance, new PolicyEvaluator())
     {
     }
 
-    public PolicyEvaluationService(PathScopeMetrics pathMetrics, ILogger<PolicyEvaluationService> logger)
+    public PolicyEvaluationService(PathScopeMetrics pathMetrics, ILogger<PolicyEvaluationService> logger, PolicyEvaluator evaluator)
     {
         _pathMetrics = pathMetrics ?? throw new ArgumentNullException(nameof(pathMetrics));
         _logger = logger ?? throw new ArgumentNullException(nameof(logger));
+        _evaluator = evaluator ?? throw new ArgumentNullException(nameof(evaluator));
     }
 
     internal Evaluation.PolicyEvaluationResult Evaluate(PolicyIrDocument document, Evaluation.PolicyEvaluationContext context)
@@ -36,7 +37,7 @@ internal sealed partial class PolicyEvaluationService
         }
 
         var request = new Evaluation.PolicyEvaluationRequest(document, context);
-        return evaluator.Evaluate(request);
+        return _evaluator.Evaluate(request);
     }
 
     // PathScopeSimulationService partial class relies on _pathMetrics.