feat: add multi-threaded evaluation benchmark suite with comprehensive C# implementation (#457)

This commit introduces a complete multi-threaded evaluation benchmark suite for both Rust and C# implementations of Regorus.

- Implemented engine evaluation benchmark with input and engine cloning strategies
- Implemented compiled policy evaluation benchmark with input cloning and shared compiled policy strategies.

- Created EngineEvaluationBenchmark.cs and CompiledPolicyEvaluationBenchmark.cs with time-based execution (3s warmup + 3s evaluation)
- Implemented configuration options matching Rust implementation (useClonedEngines, useSharedPolicies parameters)

- Created markdown analysis documentation with cross-platform performance analysis
- C# seems to achieve 58-89% of Rust performance on test machine.

Signed-off-by: Anand Krishnamoorthi <anakrish@microsoft.com>

bindings/csharp/Benchmarks/Program.cs

@@ -0,0 +1,36 @@
+using System;
+
+namespace Benchmarks
+{
+    class Program
+    {
+        static void Main(string[] args)
+        {
+            Console.WriteLine("=== Regorus C# Benchmarks ===\n");
+            
+            try
+            {
+                Console.WriteLine("Running Engine Evaluation Benchmark...");
+                EngineEvaluationBenchmark.RunEngineEvaluationBenchmark();
+            }
+            catch (Exception ex)
+            {
+                Console.WriteLine($"Engine benchmark failed: {ex.Message}");
+            }
+            
+            Console.WriteLine("\n" + new string('=', 80) + "\n");
+            
+            try
+            {
+                Console.WriteLine("Running Compiled Policy Evaluation Benchmark...");
+                CompiledPolicyEvaluationBenchmark.RunCompiledPolicyEvaluationBenchmark();
+            }
+            catch (Exception ex)
+            {
+                Console.WriteLine($"Compiled policy benchmark failed: {ex.Message}");
+            }
+            
+            Console.WriteLine("\n=== Benchmarks Complete ===");
+        }
+    }
+}