refactor: split EpubService into EpubReaderService and EpubMetadataExtractor (SRP)

src/NexusReader.Infrastructure/Services/EpubService.cs

@@ -10,13 +10,13 @@ using NexusReader.Domain.Entities;
 
 namespace NexusReader.Infrastructure.Services;
 
-public class EpubService : IEpubService
+public class EpubReaderService : IEpubReader
 {
     private readonly IDbContextFactory<AppDbContext> _dbContextFactory;
     private const string EpubPath = "wwwroot/assets/book.epub";
     private const int WordThreshold = 1000;
 
-    public EpubService(IDbContextFactory<AppDbContext> dbContextFactory)
+    public EpubReaderService(IDbContextFactory<AppDbContext> dbContextFactory)
     {
         _dbContextFactory = dbContextFactory;
     }
@@ -215,6 +215,10 @@ public class EpubService : IEpubService
         }
         return null;
     }
+}
+
+public class EpubMetadataExtractor : IEpubMetadataExtractor
+{
     public async Task<Result<LocalEpubMetadata>> ExtractMetadataAsync(Stream epubStream)
     {
         try