refactor: split jikan client into smaller domain files

internal/jikan/anime.go

@@ -0,0 +1,19 @@
+package jikan
+
+import "fmt"
+
+// GetAnimeByID fetches full details for a single anime
+func (c *Client) GetAnimeByID(id int) (Anime, error) {
+	if cached, ok := c.animeCache.Get(id); ok {
+		return cached, nil
+	}
+
+	var result AnimeResponse
+	reqURL := fmt.Sprintf("%s/anime/%d/full", c.baseURL, id)
+	if err := c.fetchWithRetry(reqURL, &result); err != nil {
+		return Anime{}, err
+	}
+
+	c.animeCache.Add(id, result.Data)
+	return result.Data, nil
+}