Add caption, add cache update on get

src/app/services/caption_getter.py

@@ -0,0 +1,33 @@
+from app.services.library_client import Book, BookAuthor
+
+
+def get_author_string(author: BookAuthor) -> str:
+    author_parts = []
+
+    if author.last_name:
+        author_parts.append(author.last_name)
+    
+    if author.first_name:
+        author_parts.append(author.first_name)
+    
+    if author.middle_name:
+        author_parts.append(author.middle_name)
+
+    return " ".join(author_parts)
+
+
+def get_caption(book: Book) -> str:
+    caption_title = f"📖 {book.title}"
+
+    caption_authors_parts = []
+    for author in book.authors:
+        caption_authors_parts.append(
+            f"👤 {get_author_string(author)}"
+        )
+    
+    if not caption_authors_parts:
+        return caption_title
+    
+    caption_authors = "\n".join(caption_authors_parts)
+
+    return caption_title + "\n\n" + caption_authors