feat(rate-limiting): Implement core rate limiting functionality with configuration, decision-making, metrics, middleware, and service registration

- Add RateLimitConfig for configuration management with YAML binding support.
- Introduce RateLimitDecision to encapsulate the result of rate limit checks.
- Implement RateLimitMetrics for OpenTelemetry metrics tracking.
- Create RateLimitMiddleware for enforcing rate limits on incoming requests.
- Develop RateLimitService to orchestrate instance and environment rate limit checks.
- Add RateLimitServiceCollectionExtensions for dependency injection registration.

bench/proof-chain/Program.cs

@@ -0,0 +1,21 @@
+// -----------------------------------------------------------------------------
+// Program.cs
+// Sprint: SPRINT_0501_0001_0001_proof_evidence_chain_master
+// Task: PROOF-MASTER-0005
+// Description: Benchmark suite entry point for proof chain performance
+// -----------------------------------------------------------------------------
+
+using BenchmarkDotNet.Running;
+
+namespace StellaOps.Bench.ProofChain;
+
+/// <summary>
+/// Entry point for proof chain benchmark suite.
+/// </summary>
+public class Program
+{
+    public static void Main(string[] args)
+    {
+        var summary = BenchmarkSwitcher.FromAssembly(typeof(Program).Assembly).Run(args);
+    }
+}