text: Title: [ENH] Make all collection and series transformer files private, access through init
  Body: ### Describe the feature or idea you want to propose
  
  currently like this
  ![image](https://github.com/user-attachments/assets/71194a8f-a11f-4e98-8ee2-2ace3693eef5)
  should be like series transformers 
  ![image](https://github.com/user-attachments/assets/51d33cbb-b4ad-40a7-869b-8f76b351a845)
  
  
  ### Describe your proposed solution
  
  make files private, import through init
  