refactor: create BookCommonService for shared book operations

src/main/java/ru/cathub/telegabot/service/BookCommonService.java

@@ -0,0 +1,10 @@
+package ru.cathub.telegabot.service;
+
+import ru.cathub.telegabot.model.Book;
+import ru.cathub.telegabot.model.BotUser;
+
+public interface BookCommonService {
+    void validateUser(BotUser user);
+    void clearUserBookCaches(Long userId);
+    String formatBookDetails(Book book);
+}

src/main/java/ru/cathub/telegabot/service/impl/BookCommonServiceImpl.java

@@ -0,0 +1,34 @@
+package ru.cathub.telegabot.service.impl;
+
+import lombok.RequiredArgsConstructor;
+import org.springframework.stereotype.Service;
+import ru.cathub.telegabot.model.Book;
+import ru.cathub.telegabot.model.BotUser;
+import ru.cathub.telegabot.service.BookCacheService;
+import ru.cathub.telegabot.service.BookCommonService;
+import ru.cathub.telegabot.utils.BookFormatUtils;
+
+@Service
+@RequiredArgsConstructor
+public class BookCommonServiceImpl implements BookCommonService {
+
+    private final BookCacheService bookCacheService;
+
+    @Override
+    public void validateUser(BotUser user) {
+        if (user == null) {
+            throw new IllegalArgumentException("User cannot be null");
+        }
+    }
+
+    @Override
+    public void clearUserBookCaches(Long userId) {
+        bookCacheService.clearBookListCache(userId);
+        bookCacheService.clearBookEditCache(userId);
+    }
+
+    @Override
+    public String formatBookDetails(Book book) {
+        return BookFormatUtils.formatBookEntry(book, 0, false);
+    }
+}