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/Benchmarks/IdGenerationBenchmarks.cs

@@ -0,0 +1,137 @@
+// -----------------------------------------------------------------------------
+// IdGenerationBenchmarks.cs
+// Sprint: SPRINT_0501_0001_0001_proof_evidence_chain_master
+// Task: PROOF-MASTER-0005
+// Description: Benchmarks for content-addressed ID generation
+// -----------------------------------------------------------------------------
+
+using System.Security.Cryptography;
+using System.Text;
+using System.Text.Json;
+using BenchmarkDotNet.Attributes;
+
+namespace StellaOps.Bench.ProofChain.Benchmarks;
+
+/// <summary>
+/// Benchmarks for content-addressed ID generation operations.
+/// Target: Evidence ID generation < 50μs for 10KB payload.
+/// </summary>
+[MemoryDiagnoser]
+[SimpleJob(warmupCount: 3, iterationCount: 10)]
+public class IdGenerationBenchmarks
+{
+    private byte[] _smallPayload = null!;
+    private byte[] _mediumPayload = null!;
+    private byte[] _largePayload = null!;
+    private string _canonicalJson = null!;
+    private Dictionary<string, object> _bundleData = null!;
+
+    [GlobalSetup]
+    public void Setup()
+    {
+        // Small: 1KB
+        _smallPayload = new byte[1024];
+        RandomNumberGenerator.Fill(_smallPayload);
+
+        // Medium: 10KB
+        _mediumPayload = new byte[10 * 1024];
+        RandomNumberGenerator.Fill(_mediumPayload);
+
+        // Large: 100KB
+        _largePayload = new byte[100 * 1024];
+        RandomNumberGenerator.Fill(_largePayload);
+
+        // Canonical JSON for bundle ID generation
+        _bundleData = new Dictionary<string, object>
+        {
+            ["statements"] = Enumerable.Range(0, 5).Select(i => new
+            {
+                statementId = $"sha256:{Guid.NewGuid():N}",
+                predicateType = "evidence.stella/v1",
+                predicate = new { index = i, data = Convert.ToBase64String(_smallPayload) }
+            }).ToList(),
+            ["signatures"] = new[]
+            {
+                new { keyId = "key-1", algorithm = "ES256" },
+                new { keyId = "key-2", algorithm = "ES256" }
+            }
+        };
+
+        _canonicalJson = JsonSerializer.Serialize(_bundleData, new JsonSerializerOptions
+        {
+            PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
+            WriteIndented = false
+        });
+    }
+
+    /// <summary>
+    /// Baseline: Generate evidence ID from small (1KB) payload.
+    /// Target: < 20μs
+    /// </summary>
+    [Benchmark(Baseline = true)]
+    public string GenerateEvidenceId_Small()
+    {
+        return GenerateContentAddressedId(_smallPayload, "evidence");
+    }
+
+    /// <summary>
+    /// Generate evidence ID from medium (10KB) payload.
+    /// Target: < 50μs
+    /// </summary>
+    [Benchmark]
+    public string GenerateEvidenceId_Medium()
+    {
+        return GenerateContentAddressedId(_mediumPayload, "evidence");
+    }
+
+    /// <summary>
+    /// Generate evidence ID from large (100KB) payload.
+    /// Target: < 200μs
+    /// </summary>
+    [Benchmark]
+    public string GenerateEvidenceId_Large()
+    {
+        return GenerateContentAddressedId(_largePayload, "evidence");
+    }
+
+    /// <summary>
+    /// Generate proof bundle ID from JSON content.
+    /// Target: < 500μs
+    /// </summary>
+    [Benchmark]
+    public string GenerateProofBundleId()
+    {
+        return GenerateContentAddressedId(Encoding.UTF8.GetBytes(_canonicalJson), "bundle");
+    }
+
+    /// <summary>
+    /// Generate SBOM entry ID (includes PURL formatting).
+    /// Target: < 30μs
+    /// </summary>
+    [Benchmark]
+    public string GenerateSbomEntryId()
+    {
+        var digest = "sha256:" + Convert.ToHexString(SHA256.HashData(_smallPayload)).ToLowerInvariant();
+        var purl = "pkg:npm/%40scope/package@1.0.0";
+        return $"{digest}:{purl}";
+    }
+
+    /// <summary>
+    /// Generate reasoning ID with timestamp.
+    /// Target: < 25μs
+    /// </summary>
+    [Benchmark]
+    public string GenerateReasoningId()
+    {
+        var timestamp = DateTimeOffset.UtcNow.ToString("O");
+        var input = Encoding.UTF8.GetBytes($"reasoning:{timestamp}:{_canonicalJson}");
+        var hash = SHA256.HashData(input);
+        return $"sha256:{Convert.ToHexString(hash).ToLowerInvariant()}";
+    }
+
+    private static string GenerateContentAddressedId(byte[] content, string prefix)
+    {
+        var hash = SHA256.HashData(content);
+        return $"sha256:{Convert.ToHexString(hash).ToLowerInvariant()}";
+    }
+}