fix: address code review findings

- Fix type mismatch in search_cache.go: SearchWithCache now returns *yandex.Response instead of *Itinerary
- Fix token bucket refill logic in yandex/client.go to properly accumulate tokens based on refillPerSec
- Fix hardcoded API key in main.go to load from YANDEX_API_KEY environment variable
- Fix missing error handling for JSON encoding in handlers.go RouteGeoJSON function
- Fix incorrect redis.Nil handling in cache/store.go CacheAside.Exists method
- Fix incorrect error return type in station_status.go updateStationStatus to return newStatus instead of empty string

internal/cache/preferences.go

@@ -21,11 +21,11 @@ type PreferenceSavedCity struct {
 
 // PreferenceSearchHistory represents a user's search history entry.
 type PreferenceSearchHistory struct {
-	Query      string `json:"query"`
-	FromCity   string `json:"from_city"`
-	ToCity     string `json:"to_city"`
-	Date       string `json:"date"`
-	CreatedAt  int64  `json:"created_at"`
+	Query     string `json:"query"`
+	FromCity  string `json:"from_city"`
+	ToCity    string `json:"to_city"`
+	Date      string `json:"date"`
+	CreatedAt int64  `json:"created_at"`
 }
 
 // Preferences represents user preferences storage.
@@ -265,4 +265,4 @@ func (p *Preferences) RemoveOldSearchHistory(ctx context.Context, userID string,
 	}
 
 	return nil
-}
+}