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/Events/FeedEpochAdvancedEvent.cs

@@ -80,6 +80,17 @@ public sealed record FeedEpochAdvancedEvent
     /// <summary>
     /// Creates a new FeedEpochAdvancedEvent.
     /// </summary>
+    /// <param name="feedId">The feed identifier.</param>
+    /// <param name="previousEpoch">The previous epoch identifier.</param>
+    /// <param name="newEpoch">The new epoch identifier.</param>
+    /// <param name="effectiveAt">When the new epoch became effective.</param>
+    /// <param name="advisoriesAdded">Number of advisories added (for metrics).</param>
+    /// <param name="advisoriesModified">Number of advisories modified (for metrics).</param>
+    /// <param name="advisoriesWithdrawn">Number of advisories withdrawn (for metrics).</param>
+    /// <param name="tenantId">Tenant ID if multi-tenant.</param>
+    /// <param name="correlationId">Correlation ID for tracing.</param>
+    /// <param name="eventId">Optional event ID (defaults to new GUID).</param>
+    /// <param name="timestamp">Optional timestamp (defaults to current UTC time).</param>
     public static FeedEpochAdvancedEvent Create(
         string feedId,
         string previousEpoch,
@@ -89,12 +100,14 @@ public sealed record FeedEpochAdvancedEvent
         int? advisoriesModified = null,
         int? advisoriesWithdrawn = null,
         string? tenantId = null,
-        string? correlationId = null)
+        string? correlationId = null,
+        Guid? eventId = null,
+        DateTimeOffset? timestamp = null)
     {
         return new FeedEpochAdvancedEvent
         {
-            EventId = Guid.NewGuid(),
-            Timestamp = DateTimeOffset.UtcNow,
+            EventId = eventId ?? Guid.NewGuid(),
+            Timestamp = timestamp ?? DateTimeOffset.UtcNow,
             FeedId = feedId,
             PreviousEpoch = previousEpoch,
             NewEpoch = newEpoch,