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/StellaOps.Provcache.csproj

@@ -25,6 +25,7 @@
   <ItemGroup>
     <ProjectReference Include="../StellaOps.Canonical.Json/StellaOps.Canonical.Json.csproj" />
     <ProjectReference Include="../StellaOps.Cryptography/StellaOps.Cryptography.csproj" />
+    <ProjectReference Include="../StellaOps.Determinism.Abstractions/StellaOps.Determinism.Abstractions.csproj" />
     <ProjectReference Include="../../Router/__Libraries/StellaOps.Messaging/StellaOps.Messaging.csproj" />
     <ProjectReference Include="../../Provenance/StellaOps.Provenance.Attestation/StellaOps.Provenance.Attestation.csproj" />
   </ItemGroup>