refactor(provcache): inject TimeProvider and IGuidProvider for determinism - DET-005

Refactored 8 files across StellaOps.Provcache, StellaOps.Provcache.Postgres, and StellaOps.Provcache.Valkey:

Core Provcache library:
- EvidenceChunker: Added IGuidProvider for ChunkId generation in ChunkAsync/ChunkStreamAsync
- LazyFetchOrchestrator: Added IGuidProvider for ChunkId generation when storing fetched chunks
- MinimalProofExporter: Added IGuidProvider for ChunkId generation in ImportAsync
- FeedEpochAdvancedEvent: Added optional eventId/timestamp parameters to static Create()
- SignerRevokedEvent: Added optional eventId/timestamp parameters to static Create()

Postgres implementation:
- PostgresProvcacheRepository: Added TimeProvider and IGuidProvider for IncrementHitCountAsync,
  GetStatisticsAsync, LogRevocationAsync, and MapToEntity
- PostgresEvidenceChunkRepository: Added TimeProvider and IGuidProvider for GetManifestAsync and MapToEntity

Valkey implementation:
- ValkeyProvcacheStore: Added TimeProvider for TTL calculations in GetAsync, SetAsync, SetManyAsync

All constructors use optional parameters with defaults to system implementations for backward compatibility.
Added StellaOps.Determinism.Abstractions project references where needed.

src/__Libraries/StellaOps.Provcache/LazyFetch/LazyFetchOrchestrator.cs

@@ -1,6 +1,7 @@
 using System.Diagnostics;
 using System.Security.Cryptography;
 using Microsoft.Extensions.Logging;
+using StellaOps.Determinism;
 
 namespace StellaOps.Provcache;
 
@@ -13,6 +14,7 @@ public sealed class LazyFetchOrchestrator
     private readonly IEvidenceChunkRepository _repository;
     private readonly ILogger<LazyFetchOrchestrator> _logger;
     private readonly TimeProvider _timeProvider;
+    private readonly IGuidProvider _guidProvider;
 
     /// <summary>
     /// Creates a lazy fetch orchestrator.
@@ -20,14 +22,17 @@ public sealed class LazyFetchOrchestrator
     /// <param name="repository">The chunk repository for local storage.</param>
     /// <param name="logger">Logger instance.</param>
     /// <param name="timeProvider">Optional time provider.</param>
+    /// <param name="guidProvider">Optional GUID provider.</param>
     public LazyFetchOrchestrator(
         IEvidenceChunkRepository repository,
         ILogger<LazyFetchOrchestrator> logger,
-        TimeProvider? timeProvider = null)
+        TimeProvider? timeProvider = null,
+        IGuidProvider? guidProvider = null)
     {
         _repository = repository ?? throw new ArgumentNullException(nameof(repository));
         _logger = logger ?? throw new ArgumentNullException(nameof(logger));
         _timeProvider = timeProvider ?? TimeProvider.System;
+        _guidProvider = guidProvider ?? SystemGuidProvider.Instance;
     }
 
     /// <summary>
@@ -154,7 +159,7 @@ public sealed class LazyFetchOrchestrator
                 // Convert FetchedChunk to EvidenceChunk for storage
                 var evidenceChunk = new EvidenceChunk
                 {
-                    ChunkId = Guid.NewGuid(),
+                    ChunkId = _guidProvider.NewGuid(),
                     ProofRoot = proofRoot,
                     ChunkIndex = fetchedChunk.Index,
                     ChunkHash = fetchedChunk.Hash,