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/Chunking/EvidenceChunker.cs

@@ -1,4 +1,5 @@
 using System.Security.Cryptography;
+using StellaOps.Determinism;
 
 namespace StellaOps.Provcache;
 
@@ -87,11 +88,16 @@ public sealed class EvidenceChunker : IEvidenceChunker
 {
     private readonly ProvcacheOptions _options;
     private readonly TimeProvider _timeProvider;
+    private readonly IGuidProvider _guidProvider;
 
-    public EvidenceChunker(ProvcacheOptions options, TimeProvider? timeProvider = null)
+    public EvidenceChunker(
+        ProvcacheOptions options,
+        TimeProvider? timeProvider = null,
+        IGuidProvider? guidProvider = null)
     {
         _options = options ?? throw new ArgumentNullException(nameof(options));
         _timeProvider = timeProvider ?? TimeProvider.System;
+        _guidProvider = guidProvider ?? SystemGuidProvider.Instance;
     }
 
     /// <inheritdoc />
@@ -122,7 +128,7 @@ public sealed class EvidenceChunker : IEvidenceChunker
 
             chunks.Add(new EvidenceChunk
             {
-                ChunkId = Guid.NewGuid(),
+                ChunkId = _guidProvider.NewGuid(),
                 ProofRoot = string.Empty, // Will be set after computing Merkle root
                 ChunkIndex = chunkIndex,
                 ChunkHash = chunkHash,
@@ -171,7 +177,7 @@ public sealed class EvidenceChunker : IEvidenceChunker
 
             yield return new EvidenceChunk
             {
-                ChunkId = Guid.NewGuid(),
+                ChunkId = _guidProvider.NewGuid(),
                 ProofRoot = string.Empty, // Caller must compute after all chunks
                 ChunkIndex = chunkIndex,
                 ChunkHash = chunkHash,