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.Postgres/PostgresProvcacheRepository.cs

@@ -1,6 +1,7 @@
 using System.Text.Json;
 using Microsoft.EntityFrameworkCore;
 using Microsoft.Extensions.Logging;
+using StellaOps.Determinism;
 using StellaOps.Provcache.Entities;
 
 namespace StellaOps.Provcache.Postgres;
@@ -12,14 +13,20 @@ public sealed class PostgresProvcacheRepository : IProvcacheRepository
 {
     private readonly ProvcacheDbContext _context;
     private readonly ILogger<PostgresProvcacheRepository> _logger;
+    private readonly TimeProvider _timeProvider;
+    private readonly IGuidProvider _guidProvider;
     private readonly JsonSerializerOptions _jsonOptions;
 
     public PostgresProvcacheRepository(
         ProvcacheDbContext context,
-        ILogger<PostgresProvcacheRepository> logger)
+        ILogger<PostgresProvcacheRepository> logger,
+        TimeProvider? timeProvider = null,
+        IGuidProvider? guidProvider = null)
     {
         _context = context ?? throw new ArgumentNullException(nameof(context));
         _logger = logger ?? throw new ArgumentNullException(nameof(logger));
+        _timeProvider = timeProvider ?? TimeProvider.System;
+        _guidProvider = guidProvider ?? SystemGuidProvider.Instance;
         _jsonOptions = new JsonSerializerOptions
         {
             PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
@@ -193,12 +200,13 @@ public sealed class PostgresProvcacheRepository : IProvcacheRepository
     /// <inheritdoc />
     public async Task IncrementHitCountAsync(string veriKey, CancellationToken cancellationToken = default)
     {
+        var now = _timeProvider.GetUtcNow();
         await _context.ProvcacheItems
             .Where(e => e.VeriKey == veriKey)
             .ExecuteUpdateAsync(
                 setters => setters
                     .SetProperty(e => e.HitCount, e => e.HitCount + 1)
-                    .SetProperty(e => e.LastAccessedAt, DateTimeOffset.UtcNow),
+                    .SetProperty(e => e.LastAccessedAt, now),
                 cancellationToken)
             .ConfigureAwait(false);
     }
@@ -206,7 +214,7 @@ public sealed class PostgresProvcacheRepository : IProvcacheRepository
     /// <inheritdoc />
     public async Task<ProvcacheStatistics> GetStatisticsAsync(CancellationToken cancellationToken = default)
     {
-        var now = DateTimeOffset.UtcNow;
+        var now = _timeProvider.GetUtcNow();
         var hourFromNow = now.AddHours(1);
 
         var totalEntries = await _context.ProvcacheItems
@@ -266,12 +274,12 @@ public sealed class PostgresProvcacheRepository : IProvcacheRepository
     {
         var revocation = new ProvcacheRevocationEntity
         {
-            RevocationId = Guid.NewGuid(),
+            RevocationId = _guidProvider.NewGuid(),
             RevocationType = type,
             TargetHash = targetHash,
             Reason = reason,
             EntriesAffected = entriesAffected,
-            CreatedAt = DateTimeOffset.UtcNow
+            CreatedAt = _timeProvider.GetUtcNow()
         };
 
         _context.Revocations.Add(revocation);
@@ -329,7 +337,7 @@ public sealed class PostgresProvcacheRepository : IProvcacheRepository
             HitCount = entry.HitCount,
             CreatedAt = entry.CreatedAt,
             ExpiresAt = entry.ExpiresAt,
-            UpdatedAt = DateTimeOffset.UtcNow,
+            UpdatedAt = _timeProvider.GetUtcNow(),
             LastAccessedAt = entry.LastAccessedAt
         };
     }