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/ProofSpineAssemblyBenchmarks.cs

@@ -0,0 +1,199 @@
+// -----------------------------------------------------------------------------
+// ProofSpineAssemblyBenchmarks.cs
+// Sprint: SPRINT_0501_0001_0001_proof_evidence_chain_master
+// Task: PROOF-MASTER-0005
+// Description: Benchmarks for proof spine assembly and Merkle tree operations
+// -----------------------------------------------------------------------------
+
+using System.Security.Cryptography;
+using BenchmarkDotNet.Attributes;
+
+namespace StellaOps.Bench.ProofChain.Benchmarks;
+
+/// <summary>
+/// Benchmarks for proof spine assembly operations.
+/// Target: Spine assembly (5 items) < 5ms.
+/// </summary>
+[MemoryDiagnoser]
+[SimpleJob(warmupCount: 3, iterationCount: 10)]
+public class ProofSpineAssemblyBenchmarks
+{
+    private List<byte[]> _evidenceItems = null!;
+    private List<byte[]> _merkleLeaves = null!;
+    private byte[] _reasoning = null!;
+    private byte[] _vexVerdict = null!;
+
+    [Params(1, 5, 10, 50)]
+    public int EvidenceCount { get; set; }
+
+    [GlobalSetup]
+    public void Setup()
+    {
+        // Generate evidence items of varying sizes
+        _evidenceItems = Enumerable.Range(0, 100)
+            .Select(i =>
+            {
+                var data = new byte[1024 + (i * 100)]; // 1KB to ~10KB
+                RandomNumberGenerator.Fill(data);
+                return data;
+            })
+            .ToList();
+
+        // Merkle tree leaves
+        _merkleLeaves = Enumerable.Range(0, 100)
+            .Select(_ =>
+            {
+                var leaf = new byte[32];
+                RandomNumberGenerator.Fill(leaf);
+                return leaf;
+            })
+            .ToList();
+
+        // Reasoning and verdict
+        _reasoning = new byte[2048];
+        RandomNumberGenerator.Fill(_reasoning);
+
+        _vexVerdict = new byte[512];
+        RandomNumberGenerator.Fill(_vexVerdict);
+    }
+
+    /// <summary>
+    /// Assemble proof spine from evidence items.
+    /// Target: < 5ms for 5 items.
+    /// </summary>
+    [Benchmark]
+    public ProofSpineResult AssembleSpine()
+    {
+        var evidence = _evidenceItems.Take(EvidenceCount).ToList();
+        return AssembleProofSpine(evidence, _reasoning, _vexVerdict);
+    }
+
+    /// <summary>
+    /// Build Merkle tree from leaves.
+    /// Target: < 1ms for 100 leaves.
+    /// </summary>
+    [Benchmark]
+    public byte[] BuildMerkleTree()
+    {
+        return ComputeMerkleRoot(_merkleLeaves.Take(EvidenceCount).ToList());
+    }
+
+    /// <summary>
+    /// Generate deterministic bundle ID from spine.
+    /// Target: < 500μs.
+    /// </summary>
+    [Benchmark]
+    public string GenerateBundleId()
+    {
+        var spine = AssembleProofSpine(
+            _evidenceItems.Take(EvidenceCount).ToList(),
+            _reasoning,
+            _vexVerdict);
+        return ComputeBundleId(spine);
+    }
+
+    /// <summary>
+    /// Verify spine determinism (same inputs = same output).
+    /// </summary>
+    [Benchmark]
+    public bool VerifyDeterminism()
+    {
+        var evidence = _evidenceItems.Take(EvidenceCount).ToList();
+        var spine1 = AssembleProofSpine(evidence, _reasoning, _vexVerdict);
+        var spine2 = AssembleProofSpine(evidence, _reasoning, _vexVerdict);
+        return spine1.BundleId == spine2.BundleId;
+    }
+
+    #region Implementation
+
+    private static ProofSpineResult AssembleProofSpine(
+        List<byte[]> evidence,
+        byte[] reasoning,
+        byte[] vexVerdict)
+    {
+        // 1. Generate evidence IDs
+        var evidenceIds = evidence
+            .OrderBy(e => Convert.ToHexString(SHA256.HashData(e))) // Deterministic ordering
+            .Select(e => SHA256.HashData(e))
+            .ToList();
+
+        // 2. Build Merkle tree
+        var merkleRoot = ComputeMerkleRoot(evidenceIds);
+
+        // 3. Compute reasoning ID
+        var reasoningId = SHA256.HashData(reasoning);
+
+        // 4. Compute verdict ID
+        var verdictId = SHA256.HashData(vexVerdict);
+
+        // 5. Assemble bundle content
+        var bundleContent = new List<byte>();
+        bundleContent.AddRange(merkleRoot);
+        bundleContent.AddRange(reasoningId);
+        bundleContent.AddRange(verdictId);
+
+        // 6. Compute bundle ID
+        var bundleId = SHA256.HashData(bundleContent.ToArray());
+
+        return new ProofSpineResult
+        {
+            BundleId = $"sha256:{Convert.ToHexString(bundleId).ToLowerInvariant()}",
+            MerkleRoot = merkleRoot,
+            EvidenceIds = evidenceIds.Select(e => $"sha256:{Convert.ToHexString(e).ToLowerInvariant()}").ToList()
+        };
+    }
+
+    private static byte[] ComputeMerkleRoot(List<byte[]> leaves)
+    {
+        if (leaves.Count == 0)
+            return SHA256.HashData(Array.Empty<byte>());
+
+        if (leaves.Count == 1)
+            return leaves[0];
+
+        var currentLevel = leaves.ToList();
+
+        while (currentLevel.Count > 1)
+        {
+            var nextLevel = new List<byte[]>();
+
+            for (int i = 0; i < currentLevel.Count; i += 2)
+            {
+                if (i + 1 < currentLevel.Count)
+                {
+                    // Hash pair
+                    var combined = new byte[currentLevel[i].Length + currentLevel[i + 1].Length];
+                    currentLevel[i].CopyTo(combined, 0);
+                    currentLevel[i + 1].CopyTo(combined, currentLevel[i].Length);
+                    nextLevel.Add(SHA256.HashData(combined));
+                }
+                else
+                {
+                    // Odd node - promote
+                    nextLevel.Add(currentLevel[i]);
+                }
+            }
+
+            currentLevel = nextLevel;
+        }
+
+        return currentLevel[0];
+    }
+
+    private static string ComputeBundleId(ProofSpineResult spine)
+    {
+        return spine.BundleId;
+    }
+
+    #endregion
+}
+
+/// <summary>
+/// Result of proof spine assembly.
+/// </summary>
+public sealed class ProofSpineResult
+{
+    public required string BundleId { get; init; }
+    public required byte[] MerkleRoot { get; init; }
+    public required List<string> EvidenceIds { get; init; }
+}